Remove duplicate entry in ./Documentation/Makefile

Signed-off-by: Thomas Ackermann <th.acker@arcor.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/Makefile

@@ -31,7 +31,6 @@ SP_ARTICLES += howto/separating-topic-branches
 SP_ARTICLES += howto/revert-a-faulty-merge
 SP_ARTICLES += howto/recover-corrupted-blob-object
 SP_ARTICLES += howto/rebuild-from-update-hook
-SP_ARTICLES += howto/rebuild-from-update-hook
 SP_ARTICLES += howto/rebase-from-internal-branch
 SP_ARTICLES += howto/maintain-git
 API_DOCS = $(patsubst %.txt,%,$(filter-out technical/api-index-skel.txt technical/api-index.txt, $(wildcard technical/api-*.txt)))