completion: delete option-only completion commands

The new function __git_complete_common can take over this job with
less code to maintain.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/completion/git-completion.bash

@@ -1505,16 +1505,6 @@ _git_fsck ()
 	esac
 }
 
-_git_gc ()
-{
-	case "$cur" in
-	--*)
-		__gitcomp_builtin gc
-		return
-		;;
-	esac
-}
-
 _git_gitk ()
 {
 	_gitk
@@ -1814,11 +1804,6 @@ _git_mv ()
 	fi
 }
 
-_git_name_rev ()
-{
-	__gitcomp_builtin name-rev
-}
-
 _git_notes ()
 {
 	local subcommands='add append copy edit get-ref list merge prune remove show'