Merge branch 'sg/completion-no-column' into maint

The completion script (in contrib/) used to list "git column"
(which is not an end-user facing command) as one of the choices

* sg/completion-no-column:
  completion: remove 'git column' from porcelain commands

contrib/completion/git-completion.bash

@@ -663,6 +663,7 @@ __git_list_porcelain_commands ()
 		check-mailmap)    : plumbing;;
 		check-ref-format) : plumbing;;
 		checkout-index)   : plumbing;;
+		column)           : internal helper;;
 		commit-tree)      : plumbing;;
 		count-objects)    : infrequent;;
 		credential)       : credentials;;