Build: suppress deprecated JVM target warning globally

There seems to be no point in configuring the compiler argument per
project. This argument will be deleted soon anyway, when we remove
support for JDK 1.6 & 1.7.

Also remove `disableDeprecatedJvmTargetWarning`. It didn't have any
effect in all modules where it was applied because these modules
reassign `freeCompilerArgs` anyway, with
`-Xsuppress-deprecated-jvm-target-warning` in it.

buildSrc/src/main/kotlin/LibrariesCommon.kt

@@ -9,12 +9,8 @@ import org.gradle.api.JavaVersion
 import org.gradle.api.Project
 import org.gradle.api.file.FileCollection
 import org.gradle.api.tasks.compile.JavaCompile
-import org.gradle.kotlin.dsl.extra
 import org.gradle.kotlin.dsl.get
-import org.gradle.kotlin.dsl.provideDelegate
-import org.gradle.kotlin.dsl.withType
 import org.gradle.process.CommandLineArgumentProvider
-import org.jetbrains.kotlin.gradle.tasks.KotlinCompile
 
 @JvmOverloads
 fun Project.configureJava9Compilation(
@@ -59,17 +55,3 @@ private class Java9AdditionalArgumentsProvider(
         "-Xlint:-requires-transitive-automatic" // suppress automatic module transitive dependencies in kotlin.test
     )
 }
-
-fun Project.disableDeprecatedJvmTargetWarning() {
-    if (!kotlinBuildProperties.disableWerror) {
-        val tasksWithWarnings: List<String> by rootProject.extra
-        tasks.withType<KotlinCompile>().configureEach {
-            if (!tasksWithWarnings.contains(path)) {
-                kotlinOptions {
-                    allWarningsAsErrors = true
-                    freeCompilerArgs += "-Xsuppress-deprecated-jvm-target-warning"
-                }
-            }
-        }
-    }
-}