Get rid of FIELD_IDENTIFIER at syntax level, two errors dropped, a set of tests fixed / deleted #KT-9539 Fixed

idea/idea-completion/testData/basic/common/CompletionInSetter.kt

@@ -1,9 +1,9 @@
 val a: Int = 1
     get() {
-      return $a
+      return field
     }
     set(v) {
-      $a = <caret>
+      field = <caret>
     }