[git] Add completion for gbx and gbX

that use the git-branch-delete-interactive function.

Thanks to @Mikachu for helping with the completion function
implementation over the #zsh chat.

Closes #265

modules/git/functions/_git-branch-delete-interactive

@@ -0,0 +1,3 @@
+#compdef git-branch-delete-interactive
+
+words[1]=(git branch); (( CURRENT++ )); service=git; _git

modules/git/functions/git-branch-delete-interactive

@@ -1,6 +1,6 @@
 # vim:et sts=2 sw=2 ft=zsh
 local -a remotes
-if (( ${*[(I)-r]} || ${*[(I)--remotes]} )); then
+if (( ${*[(I)(-r|--remotes)]} )); then
   remotes=(${^*:#-*})
 else
   remotes=(${(f)"$(command git rev-parse --abbrev-ref ${^*:#-*}@{u} 2>/dev/null)"})