refactor(memory): use builtin strcat() instead of STRCAT()

The latter was mostly relevant with the past char_u madness.

NOTE: STRCAT also functioned as a counterfeit "NOLINT" for clint
apparently. But NOLINT-ing every usecase is just the same as disabling
the check entirely.

src/nvim/syntax.c

@@ -4992,7 +4992,7 @@ static int get_id_list(char **const arg, const int keylen, int16_t **const list,
         } else {
           // Handle match of regexp with group names.
           *name = '^';
-          STRCAT(name, "$");
+          strcat(name, "$");
           regmatch.regprog = vim_regcomp(name, RE_MAGIC);
           if (regmatch.regprog == NULL) {
             failed = true;