dosutils: use shared option helper functions

Replace small local option helper wrappers with the shared tools.c helpers.

SLIST now uses tool_is_help_arg() directly, and REMOVE/REVOKE use
tool_is_files_option() and tool_is_subdirs_option() instead of Trustee-specific
wrappers. This keeps trustee.c focused on Rights/Trustee behavior and leaves
generic command-line option handling in tools.c.

No behavior change.

remove.c

@@ -260,13 +260,13 @@ int func_remove(int argc, char *argv[], int mode)
       return(1);
     }
 
-    if (trustee_is_files_option(argv[i])) {
+    if (tool_is_files_option(argv[i])) {
       use_files = 1;
       i++;
       continue;
     }
 
-    if (trustee_is_subdirs_option(argv[i])) {
+    if (tool_is_subdirs_option(argv[i])) {
       use_subdirs = 1;
       i++;
       continue;