Remove idea/src/META-INF/extensions/{kotlin2jvm.xml,kotlin2js.xml}

Keep the EnvironmentConfigFiles enum because its values are used in
determining whether the environment is going to be used for JVM or
non-JVM project analysis, but remove the actual files.

Drop EnvironmentConfigFiles.EMPTY and replace its only usage in
preprocessor with JVM_CONFIG_FILES: it's easier and won't affect
anything

compiler/conditional-preprocessor/src/org.jetbrains.kotlin.preprocessor/Preprocessor.kt

@@ -52,7 +52,7 @@ class Preprocessor(val logger: Logger = SystemOutLogger) {
 
     init {
         val configuration = CompilerConfiguration()
-        val environment = KotlinCoreEnvironment.createForProduction(Disposable {  }, configuration, EnvironmentConfigFiles.EMPTY)
+        val environment = KotlinCoreEnvironment.createForProduction(Disposable {  }, configuration, EnvironmentConfigFiles.JVM_CONFIG_FILES)
 
         val project = environment.project
         jetPsiFactory = KtPsiFactory(project)