packfile: remove unused member from struct pack_entry

The sha1 member in struct pack_entry is unused except for one instance
in which we store a value in it.  Since nobody ever reads this value,
don't bother to compute it and remove the member from struct pack_entry.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

cache.h

@@ -1572,7 +1572,6 @@ struct pack_window {
 
 struct pack_entry {
 	off_t offset;
-	unsigned char sha1[20];
 	struct packed_git *p;
 };
 

packfile.c

@@ -1833,7 +1833,6 @@ static int fill_pack_entry(const unsigned char *sha1,
 		return 0;
 	e->offset = offset;
 	e->p = p;
-	hashcpy(e->sha1, sha1);
 	return 1;
 }