move duplicated get_local_heads() to remote.c

move duplicated get_local_heads() to remote.c

get_local_heads() appears to have been copied from builtin-send-pack.c
to http-push.c via cut and paste. This patch moves the function and its
helper one_local_ref() to remote.c.

The two copies of one_local_ref() were not identical. I used the more
recent version from builtin-send-pack.c after confirming with Jeff King
that it was an oversight that commit 30affa1e did not update both
copies.

This is in preparation for being able to call it from builtin-remote.c

Signed-off-by: Jay Soffian <jaysoffian@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>