Makefile: remove redundant object in git-http{fetch,push}

revision.o is included in libgit.a which is in $(GITLIBS), so we don't
need to include is separately.  This fixes compilation with
"-fwhole-program" which otherwise fails with messages like this:

  libgit.a(revision.o): In function `mark_tree_uninteresting':
  /home/john/src/git/revision.c:108: multiple definition of `mark_tree_uninteresting'
  /tmp/ccKQRkZV.ltrans2.ltrans.o:/home/john/src/git/revision.c:108: first defined here

Signed-off-by: John Keeping <john@keeping.me.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Makefile

@@ -2044,10 +2044,10 @@ git-imap-send$X: imap-send.o GIT-LDFLAGS $(GITLIBS)
 	$(QUIET_LINK)$(CC) $(ALL_CFLAGS) -o $@ $(ALL_LDFLAGS) $(filter %.o,$^) \
 		$(LIBS) $(OPENSSL_LINK) $(OPENSSL_LIBSSL) $(LIB_4_CRYPTO)
 
-git-http-fetch$X: revision.o http.o http-walker.o http-fetch.o GIT-LDFLAGS $(GITLIBS)
+git-http-fetch$X: http.o http-walker.o http-fetch.o GIT-LDFLAGS $(GITLIBS)
 	$(QUIET_LINK)$(CC) $(ALL_CFLAGS) -o $@ $(ALL_LDFLAGS) $(filter %.o,$^) \
 		$(LIBS) $(CURL_LIBCURL)
-git-http-push$X: revision.o http.o http-push.o GIT-LDFLAGS $(GITLIBS)
+git-http-push$X: http.o http-push.o GIT-LDFLAGS $(GITLIBS)
 	$(QUIET_LINK)$(CC) $(ALL_CFLAGS) -o $@ $(ALL_LDFLAGS) $(filter %.o,$^) \
 		$(LIBS) $(CURL_LIBCURL) $(EXPAT_LIBEXPAT)