do not search functions for patch ID

Visual aids, such as the function name in the hunk
header, are not necessary for the purposes of
computing a patch ID.

This is a performance optimization.
Signed-off-by: NClemens Buchacher <drizzd@aon.at>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

diff.c

@@ -3768,7 +3768,7 @@ static int diff_get_patch_id(struct diff_options *options, unsigned char *sha1)
 
 		xpp.flags = 0;
 		xecfg.ctxlen = 3;
-		xecfg.flags = XDL_EMIT_FUNCNAMES;
+		xecfg.flags = 0;
 		xdi_diff_outf(&mf1, &mf2, patch_id_consume, &data,
 			      &xpp, &xecfg);
 	}