string(JSON): fix error message on invalid mode

The `GET_ARRAY` and `MEMBERS` modes were removed during development and
review of commit 8eab76eb84 (string(JSON): Adds JSON parsing support to
the string command, 2020-08-24, v3.19.0-rc1~159^2), but were
accidentally left in an error message.

Source/cmStringCommand.cxx

@@ -1106,8 +1106,8 @@ bool HandleJSONCommand(std::vector<std::string> const& arguments,
         mode != "EQUAL"_s) {
       throw json_error(
         { "got an invalid mode '"_s, mode,
-          "', expected one of GET, GET_ARRAY, TYPE, MEMBER, MEMBERS,"
-          " LENGTH, REMOVE, SET, EQUAL"_s });
+          "', expected one of GET, TYPE, MEMBER, LENGTH, REMOVE, SET, "
+          " EQUAL"_s });
     }
 
     const auto& jsonstr = args.PopFront("missing json string argument"_s);

Tests/RunCMake/string/JSONWrongMode-stderr.txt

@@ -1,5 +1,5 @@
 CMake Error at JSONWrongMode.cmake:1 \(string\):
   string sub-command JSON got an invalid mode 'FOO', expected one of GET,
-  GET_ARRAY, TYPE, MEMBER, MEMBERS, LENGTH, REMOVE, SET, EQUAL.
+  TYPE, MEMBER, LENGTH, REMOVE, SET, EQUAL.
 Call Stack \(most recent call first\):
   CMakeLists\.txt:[0-9]+ \(include\)