[KUP] Disable opt-in Kotlin compiler warnings (#318)

* [KUP] Disable opt-in Kotlin compiler warnings

It was decided to deprecate and phase out the concept (see KT-77721).

Author: FenstonSingel

build.gradle.kts

@@ -107,12 +107,7 @@ allprojects {
             freeCompilerArgs.addAll("-Xreport-all-warnings", "-Xrender-internal-diagnostic-names")
 
             progressiveMode = true
-
-            if (getAllWarningsAsErrorsValue(project)) {
-                allWarningsAsErrors = true
-            } else {
-                freeCompilerArgs.addAll("-Wextra", "-Xuse-fir-experimental-checkers")
-            }
+            allWarningsAsErrors = getAllWarningsAsErrorsValue(project)
 
             freeCompilerArgs.addAll(getAdditionalKotlinCompilerOptions(project))
         }

integration/src/main/kotlin/kotlinx/benchmark/integration/ProjectBuilder.kt

@@ -45,12 +45,12 @@ private val kotlin_api_version = System.getProperty("kotlin_api_version")?.let {
     "apiVersion = org.jetbrains.kotlin.gradle.dsl.KotlinVersion.fromVersion('$it')"
 }.orEmpty()
 
-private val kotlin_warnings_settings = System.getProperty("kotlin_Werror_override")?.let {
+private val kotlin_warnings_settings = System.getProperty("kotlin_Werror_override").let {
     when (it) {
-        "disable" -> "freeCompilerArgs.addAll(\"-Wextra\", \"-Xuse-fir-experimental-checkers\")"
+        "disable" -> ""
         else -> "allWarningsAsErrors = true"
     }
-} ?: false
+}
 
 private val kotlin_additional_cli_options = System.getProperty("kotlin_additional_cli_options")?.let {
     val argsList = it.split(' ').map(String::trim).filter(String::isNotBlank)