[Build] Remove the property to skip JS IR BE tests

It's no longer needed since we going to start building libraries using the new BE,
so we have to be sure that everything works well in releases branches too.

js/js.tests/build.gradle.kts

@@ -106,9 +106,6 @@ fun Test.setUpJsBoxTests(jsEnabled: Boolean, jsIrEnabled: Boolean) {
     if (!jsEnabled && jsIrEnabled) include("org/jetbrains/kotlin/js/test/ir/semantics/*")
 
     jvmArgs("-da:jdk.nashorn.internal.runtime.RecompilableScriptFunctionData") // Disable assertion which fails due to a bug in nashorn (KT-23637)
-    if (findProperty("kotlin.compiler.js.ir.tests.skip")?.toString()?.toBoolean() == true) {
-        exclude("org/jetbrains/kotlin/js/test/ir/semantics/*")
-    }
     setUpBoxTests()
 }