[K/JS] Remove the ability to run Legacy JS backend from the Gradle Plugin

libraries/kotlin.test/js/build.gradle

@@ -18,6 +18,7 @@ compileKotlin2Js {
             "-Xallow-kotlin-package",
             "-opt-in=kotlin.contracts.ExperimentalContracts",
             "-opt-in=kotlin.RequiresOptIn",
+            "-Xforce-deprecated-legacy-compiler-usage"
     ]
     kotlinOptions {
         moduleKind = "umd"
@@ -29,10 +30,10 @@ compileKotlin2Js {
 }
 
 compileTestKotlin2Js {
-    kotlinOptions.freeCompilerArgs = ["-Xallow-kotlin-package"]
     kotlinOptions {
         metaInfo = false
         moduleKind = "umd"
+        freeCompilerArgs = ["-Xallow-kotlin-package", "-Xforce-deprecated-legacy-compiler-usage"]
     }
 }
 

libraries/kotlin.test/js/it/build.gradle

@@ -28,7 +28,10 @@ buildDir = "$projectDir/build"
 
 ["compileKotlin2Js", "compileTestKotlin2Js"].forEach {
     tasks.named(it).configure {
-        kotlinOptions.moduleKind = "commonjs"
+        kotlinOptions {
+            moduleKind = "commonjs"
+            freeCompilerArgs += "-Xforce-deprecated-legacy-compiler-usage"
+        }
     }
 }