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

idea/testData/quickfix/override/nothingToOverride/noOpenSuperFunction.kt

@@ -0,0 +1,10 @@
+// "class org.jetbrains.kotlin.idea.quickfix.ChangeMemberFunctionSignatureFix" "false"
+// ERROR: 'f' overrides nothing
+open class A {
+    open fun foo() {}
+    fun f(a: Int) {}
+}
+
+class B : A(){
+    <caret>override fun f(a: String) {}
+}