Fix rebase

Author: liufengyun

compiler/src/dotty/tools/dotc/core/NameOps.scala

@@ -228,7 +228,7 @@ object NameOps {
     /** Is a function name
      *    - FunctionN for N >= 0
      */
-    def isPlainFunction: Boolean = functionArityFor(str.Function) >= 0
+    def isPlainFunction: Boolean = functionArity >= 0
 
     /** Is an context function name, i.e one of ContextFunctionN or ErasedContextFunctionN for N >= 0
      */