completion: remove duplicate block for "git commit -c"

Remove one of two consecutive, identical blocks for "git commit -c".

This was caused by a mechanical mismerge at d931e2fb25 (Merge
branch 'mp/complete-paths', 2013-02-08).  The side branch wanted to
add this block at fea16b47 but the same fix was done independently
at 685397585 already.

Signed-off-by: Mårten Kongstad <marten.kongstad@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/completion/git-completion.bash

@@ -1182,13 +1182,6 @@ _git_commit ()
 		;;
 	esac
 
-	case "$prev" in
-	-c|-C)
-		__gitcomp_nl "$(__git_refs)" "" "${cur}"
-		return
-		;;
-	esac
-
 	case "$cur" in
 	--cleanup=*)
 		__gitcomp "default strip verbatim whitespace