remote: remove dead code in read_branches_file()

remote: remove dead code in read_branches_file()

The first line of the function checks that the remote-name contains a
slash ('/'), and sets the "slash" variable accordingly.  The only caller
of read_branches_file() is remote_get_1(); the calling codepath is
guarded by valid_remote_nick(), which checks that the remote does not
contain a slash.  Therefore, the "slash" variable can never be set:
remove the dead code that assumes otherwise.

Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>