[Gradle] Remove the system property for compiler execution strategy

#KT-51831 Fixed

libraries/tools/kotlin-gradle-plugin-api/src/common/kotlin/org/jetbrains/kotlin/gradle/tasks/CompileUsingKotlinDaemon.kt

@@ -12,7 +12,7 @@ import org.gradle.api.tasks.Internal
 
 enum class KotlinCompilerExecutionStrategy(
     /**
-     * Value that should be passed for `kotlin.compiler.execution.strategy` Gradle or system property to choose the strategy
+     * Value that should be passed for `kotlin.compiler.execution.strategy` Gradle property to choose the strategy
      */
     val propertyValue: String
 ) {

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/kotlin/org/jetbrains/kotlin/gradle/ExecutionStrategyIT.kt

@@ -75,17 +75,6 @@ abstract class ExecutionStrategyIT : KGPDaemonsBaseTest() {
         )
     }
 
-    @DisplayName("Compilation via Kotlin daemon enabled using system property")
-    @GradleTest
-    fun testDaemonViaSystemProperty(gradleVersion: GradleVersion) {
-        doTestExecutionStrategy(
-            gradleVersion,
-            KotlinCompilerExecutionStrategy.DAEMON,
-            addHeapDumpOptions = false,
-            viaSystemProperty = true
-        )
-    }
-
     @DisplayName("Compilation inside Gradle daemon")
     @GradleTest
     fun testInProcess(gradleVersion: GradleVersion) {
@@ -95,16 +84,6 @@ abstract class ExecutionStrategyIT : KGPDaemonsBaseTest() {
         )
     }
 
-    @DisplayName("Compilation inside Gradle daemon enabled using system property")
-    @GradleTest
-    fun testInProcessViaSystemProperty(gradleVersion: GradleVersion) {
-        doTestExecutionStrategy(
-            gradleVersion,
-            KotlinCompilerExecutionStrategy.IN_PROCESS,
-            viaSystemProperty = true
-        )
-    }
-
     @DisplayName("Compilation via separate compiler process")
     @GradleTest
     fun testOutOfProcess(gradleVersion: GradleVersion) {
@@ -114,21 +93,10 @@ abstract class ExecutionStrategyIT : KGPDaemonsBaseTest() {
         )
     }
 
-    @DisplayName("Compilation via separate compiler process enabled via system property")
-    @GradleTest
-    fun testOutOfProcessViaSystemProperty(gradleVersion: GradleVersion) {
-        doTestExecutionStrategy(
-            gradleVersion,
-            KotlinCompilerExecutionStrategy.OUT_OF_PROCESS,
-            viaSystemProperty = true
-        )
-    }
-
     private fun doTestExecutionStrategy(
         gradleVersion: GradleVersion,
         executionStrategy: KotlinCompilerExecutionStrategy,
         addHeapDumpOptions: Boolean = true,
-        viaSystemProperty: Boolean = false
     ) {
         project(
             projectName = "kotlinBuiltins",
@@ -137,8 +105,7 @@ abstract class ExecutionStrategyIT : KGPDaemonsBaseTest() {
         ) {
             setupProject(this)
 
-            val cliArgPrefix = if (viaSystemProperty) "-D" else "-P"
-            val strategyCLIArg = "${cliArgPrefix}kotlin.compiler.execution.strategy=${executionStrategy.propertyValue}"
+            val strategyCLIArg = "-Pkotlin.compiler.execution.strategy=${executionStrategy.propertyValue}"
             val finishMessage = "Finished executing kotlin compiler using $executionStrategy strategy"
 
             build("build", strategyCLIArg) {

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/Project Path With Spaces/gradle.properties

@@ -1 +1,2 @@
-org.gradle.jvmargs=-Xmx1024m -XX:MaxPermSize=512m -Dkotlin.compiler.execution.strategy="out-of-process"
+org.gradle.jvmargs=-Xmx1024m -XX:MaxPermSize=512m
+kotlin.compiler.execution.strategy=out-of-process

libraries/tools/kotlin-gradle-plugin/src/common/kotlin/org/jetbrains/kotlin/gradle/plugin/KotlinProperties.kt

@@ -417,19 +417,7 @@ internal class PropertiesProvider private constructor(private val project: Proje
         get() = property("kotlin.daemon.jvmargs")
 
     val kotlinCompilerExecutionStrategy: KotlinCompilerExecutionStrategy
-        get() {
-            val propertyName = "kotlin.compiler.execution.strategy"
-            val gradleProperty = property(propertyName)
-            // system property is for backward compatibility
-            val value = (gradleProperty ?: System.getProperty(propertyName)?.also {
-                SingleWarningPerBuild.show(
-                    project,
-                    "The '$propertyName' system property is deprecated and will have no effect since Kotlin 1.8.0. " +
-                            "Please use the '$propertyName' project property or the `compilerExecutionStrategy` Kotlin compile task property instead."
-                )
-            })
-            return KotlinCompilerExecutionStrategy.fromProperty(value?.toLowerCase())
-        }
+        get() = KotlinCompilerExecutionStrategy.fromProperty(property("kotlin.compiler.execution.strategy")?.toLowerCase())
 
     private fun propertyWithDeprecatedVariant(propName: String, deprecatedPropName: String): String? {
         val deprecatedProperty = property(deprecatedPropName)