fetch: stop checking for NULL transport->remote in do_fetch()

fetch: stop checking for NULL transport->remote in do_fetch()

This field will never be NULL; if it were, we'd segfault earlier in the
function when we unconditionally check transport->remote->fetch_tags.
Likewise, many other functions dereference it unconditionally.

This is a small simplification, but it will make things easier as we
extend this conditional in the next patch.

Signed-off-by: Jeff King <redacted>
Signed-off-by: Junio C Hamano <redacted>