Clean-up md/rd completions:

- use __fish_list_windows_drives
- hide dependent options

share/completions/md.fish

@@ -4,7 +4,7 @@ function __md_generate_args --description 'Function to generate args'
     case '/*'
       echo -e '/?\tShow help'
     case '*'
-      wmic logicaldisk get name | tail --lines +2
+      __fish_list_windows_drives
   end
 end
 

share/functions/rd.fish

@@ -2,11 +2,14 @@ function __rd_generate_args --description 'Function to generate args'
   set --local current_token (commandline --current-token --cut-at-cursor)
   switch $current_token
     case '/*'
+      if __fish_seen_argument --windows 's'
+        echo -e '/q\tSpecify quiet mode'
+      end
+
       echo -e '/s\tDelete a directory tree
-/q\tSpecify quiet mode
 /?\tShow help'
     case '*'
-      wmic logicaldisk get name | tail --lines +2
+      __fish_list_windows_drives
   end
 end