[parser] use existing diagnose message for invalid case raw value

Author: dduan

include/swift/AST/DiagnosticsParse.def

@@ -584,8 +584,6 @@ ERROR(throw_in_function_type,type_parsing,none,
 // Enum Types
 ERROR(expected_expr_enum_case_raw_value,type_parsing,PointsToFirstBadToken,
       "expected expression after '=' in 'case'", ())
-ERROR(not_a_proper_raw_value_expression,type_parsing,none,
-      "not a proper raw value expression", ())
 ERROR(nonliteral_enum_case_raw_value,type_parsing,PointsToFirstBadToken,
       "raw value for enum case must be a literal", ())
 

lib/Parse/ParseDecl.cpp

@@ -4405,7 +4405,7 @@ ParserStatus Parser::parseDeclEnumCase(ParseDeclOptions Flags,
         return Status;
       }
       if (RawValueExpr.isNull()) {
-        diagnose(NextLoc, diag::not_a_proper_raw_value_expression);
+        diagnose(NextLoc, diag::nonliteral_enum_case_raw_value);
         Status.setIsParseError();
         return Status;
       }