[fixcode] Accept the warning fixit for extraneous duplicate parameter label.

Author: akyrtzi

lib/FrontendTool/FrontendTool.cpp

@@ -567,7 +567,8 @@ class JSONFixitWriter : public DiagnosticConsumer {
       return true;
     if (Info.ID == diag::forced_downcast_coercion.ID ||
         Info.ID == diag::forced_downcast_noop.ID ||
-        Info.ID == diag::variable_never_mutated.ID)
+        Info.ID == diag::variable_never_mutated.ID ||
+        Info.ID == diag::parameter_extraneous_double_up.ID)
       return true;
     return false;
   }

test/FixCode/fixits-apply.swift

@@ -62,3 +62,5 @@ func ftest1() {
   // Don't replace the variable name with '_'
   let myvar = 0
 }
+
+func ftest2(x x: Int) {}

test/FixCode/fixits-apply.swift.result

@@ -65,3 +65,5 @@ func ftest1() {
   // Don't replace the variable name with '_'
   let myvar = 0
 }
+
+func ftest2(x: Int) {}