Fix gradle api dependency version in variants

Common SourceSet was forcing gradle api version to be the same
in all plugin variants via 'extendsFrom(..)'.

^KT-49227 In Progress

libraries/tools/kotlin-gradle-plugin-idea/build.gradle.kts

@@ -14,11 +14,7 @@ dependencies {
     implementation(kotlinStdlib())
     testImplementation(gradleApi())
     testImplementation(gradleKotlinDsl())
-    testImplementation(project(":kotlin-gradle-plugin")) {
-        capabilities {
-            requireCapability("org.jetbrains.kotlin:kotlin-gradle-plugin-common")
-        }
-    }
+    testImplementation(project(":kotlin-gradle-plugin"))
     testImplementation(project(":kotlin-gradle-statistics"))
     testImplementation(project(":kotlin-test:kotlin-test-junit"))
 

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

@@ -99,11 +99,7 @@ class UpToDateIT : KGPBaseTest() {
         val originalPaths get() = originalCompilerCp.map { it.replace("\\", "/") }.joinToString(", ") { "'$it'" }
 
         override fun initProject(project: TestProject) = with(project) {
-            val pluginSuffix = if (project.gradleVersion < GradleVersion.version("7.0")) {
-                "kotlin_gradle_plugin"
-            } else {
-                "kotlin_gradle_plugin_gradle70"
-            }
+            val pluginSuffix = "kotlin_gradle_plugin"
             buildGradle.appendText(
                 "\nafterEvaluate { println 'compiler_cp=' + compileKotlin.getDefaultCompilerClasspath\$$pluginSuffix().toList() }"
             )