src: in-source comments and minor TLS cleanups

Renamed some internal C++ methods and properties for consistency, and
commented SSL I/O.

- Rename waiting_new_session_ after is_waiting_new_session(), instead of
  using reverse naming (new_session_wait_), and change "waiting" to
  "awaiting".
- Make TLSWrap::ClearIn() return void, the value is never used.
- Fix a getTicketKeys() cut-n-paste error. Since it doesn't use the
  arguments, remove them from the js wrapper.
- Remove call of setTicketKeys(getTicketKeys()), its a no-op.

Backport-PR-URL: https://github.com/nodejs/node/pull/27967
PR-URL: https://github.com/nodejs/node/pull/25713


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>