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

idea/testData/quickfix/changeSignature/removeUnusedExtensionParameter.kt.after

@@ -0,0 +1,9 @@
+// "Remove parameter 'x'" "true"
+
+fun Int.f() {
+
+}
+
+fun test() {
+    1.f()
+}