zsh: -d can't be used as a global option

It's only supported as a command option and the command will fail if
-d is used as a global option. Instead of completing it in the wrong
place, don't complete it at all as it can be considered an "internal"
switch (it's not mentioned in the manual).

completion/zsh/_yadm

@@ -122,7 +122,6 @@ _yadm() {
       '--yadm-encrypt[override the standard encrypt path]: :_files -/' \
       '--yadm-archive[override the standard archive path]: :_files -/' \
       '--yadm-bootstrap[override the standard bootstrap path]: :_files' \
-      '-d[print debug traces]' \
       '--help[display yadm help information]' \
       '--version[show yadm version]' \
       '(-): :->command' \