Cleanup prepare_packed_git_one to reuse install_packed_git.

There is little point in having the linked list insertion code
appearing in install_packed_git, and then again just 30 lines
further down in the same file.
Signed-off-by: NShawn O. Pearce <spearce@spearce.org>
Signed-off-by: NJunio C Hamano <junkio@cox.net>

sha1_file.c

@@ -790,8 +790,7 @@ static void prepare_packed_git_one(char *objdir, int local)
 		p = add_packed_git(path, len + namelen, local);
 		if (!p)
 			continue;
-		p->next = packed_git;
-		packed_git = p;
+		install_packed_git(p);
 	}
 	closedir(dir);
 }