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

idea/testData/quickfix/changeSignature/notEditable.kt

@@ -0,0 +1,12 @@
+// "class org.jetbrains.kotlin.idea.quickfix.RemoveFunctionParametersFix" "false"
+//ERROR: No value passed for parameter other
+
+trait StringComparable {
+    public fun compareTo(other: String): Int = 0
+}
+
+class X: Comparable<String>, StringComparable
+
+fun main(args: Array<String>) {
+    X().compareTo(<caret>)
+}