Big change in quickfix tests: no stupid test data format with "before" and "after" file prefixes

idea/testData/quickfix/override/parameterNameChangedMultipleOverrideRenamePossible.kt.after

@@ -0,0 +1,15 @@
+// "Rename parameter to match overridden method" "true"
+abstract class A {
+    abstract fun foo(arg : Int) : Int;
+}
+
+trait X {
+    fun foo(arg : Int) : Int;
+}
+
+class B : A(), X {
+    override fun foo(arg: Int) : Int {
+        val x = arg + arg
+        return arg
+    }
+}