completion: remove credential helpers from porcelain commands

Signed-off-by: NSZEDER Gábor <szeder@ira.uka.de>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

contrib/completion/git-completion.bash

@@ -846,6 +846,8 @@ __git_list_porcelain_commands ()
 		checkout-index)   : plumbing;;
 		commit-tree)      : plumbing;;
 		count-objects)    : infrequent;;
+		credential-cache) : credentials helper;;
+		credential-store) : credentials helper;;
 		cvsexportcommit)  : export;;
 		cvsimport)        : import;;
 		cvsserver)        : daemon;;