Merge branch 'jl/submodule-deinit'

There was no Porcelain way to say "I no longer am interested in
this submodule", once you express your interest in a submodule with
"submodule init".  "submodule deinit" is the way to do so.

* jl/submodule-deinit:
  submodule: add 'deinit' command

contrib/completion/git-completion.bash

@@ -2419,7 +2419,7 @@ _git_submodule ()
 {
 	__git_has_doubledash && return
 
-	local subcommands="add status init update summary foreach sync"
+	local subcommands="add status init deinit update summary foreach sync"
 	if [ -z "$(__git_find_on_cmdline "$subcommands")" ]; then
 		case "$cur" in
 		--*)