On pool redirect, don't return client ref as connection is already cleaned up

[arjan]

#717, released in 1.24.0, releases/skips the body when a custom pool is used and a redirect (30X) response is received.

However, in this case it still returns {ok, Status, Headers, Client}, leading the HTTPoison library to think it should still fetch the body, which then fails with a req_not_found error.

Reported this downstream but would prefer to have it fixed here.

[benoitc]

Closing: This PR was written for the old hackney architecture. The new gen_statem-based connection architecture (hackney 2.x) handles redirects correctly. For follow_redirect=false, the connection pid is returned and callers should use hackney:skip_body/1 to release it to the pool. See test test_307_redirect_pool_cleanup for the expected behavior.