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

idea/testData/quickfix/changeSignature/fixExtensionLambdaSignature.kt

@@ -0,0 +1,9 @@
+// "Change the signature of function literal" "true"
+
+fun foo(f: Int.(Int, Int) -> Int) {
+
+}
+
+fun test() {
+    foo { <caret>(a: Int) -> 0 }
+}