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

idea/testData/quickfix/modifiers/removeRedundantModifier2.kt

@@ -0,0 +1,8 @@
+// "Remove redundant 'open' modifier" "true"
+abstract class B() {
+    abstract fun foo()
+}
+
+abstract class A() : B() {
+    abstract <caret>open override fun foo()
+}