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

idea/testData/quickfix/expressions/unnecessaryNonNullAssertion1.kt

@@ -0,0 +1,4 @@
+// "Remove unnecessary non-null assertion (!!)" "true"
+fun test(value : Int) : Int {
+    return value<caret>!!
+}