Eliminate a set of warnings, mostly nullability ones

idea/idea-test-framework/src/org/jetbrains/kotlin/idea/test/KotlinStdJSProjectDescriptor.kt

@@ -30,7 +30,7 @@ object KotlinStdJSProjectDescriptor : KotlinLightProjectDescriptor() {
     override fun getSdk(): Sdk? = null
 
     override fun configureModule(module: Module, model: ModifiableRootModel) {
-        val configuration = JSLibraryStdDescription(module.project).createNewLibraryForTests() ?: error("Configuration should exist")
+        val configuration = JSLibraryStdDescription(module.project).createNewLibraryForTests()
 
         val editor = NewLibraryEditor(configuration.libraryType, configuration.properties)
         configuration.addRoots(editor)

idea/idea-test-framework/src/org/jetbrains/kotlin/idea/test/testUtils.kt

@@ -69,7 +69,6 @@ fun Module.configureAs(kind: ModuleKind) {
             this.configureAs(KotlinStdJSProjectDescriptor)
         }
 
-        else -> throw IllegalArgumentException("Unknown kind=$kind")
     }
 }