Remove timeout on receiving messages on public Conn.

Summary: Since pings/pongs are handled by the underlying private conn, it was superfluous and actually wrong since keepalives are not sent on the public Conn

Test Plan: manual. unit tests pass.

Reviewers: ben, joy

Reviewed By: joy

Subscribers: joy, Engineering

Differential Revision: https://phabricator.poptip.com/D3058