libpq: Remove deprecated connection parameters authtype and tty

libpq: Remove deprecated connection parameters authtype and tty

The authtype parameter was deprecated and made inactive in commit
d5bbe2aca55bc8, but the environment variable was left defined and thus
tested with a getenv call even though the value is of no use.  Also,
if it would exist it would be copied but never freed as the cleanup
code had been removed.

tty was deprecated in commit cb7fb3ca958ec8bd5a14e7 but most of the
infrastructure around it remained in place.

Author: Daniel Gustafsson <[email protected]>
Discussion: https://postgr.es/m/DDDF36F3-582A-4C02-8598-9B464CC42B34@yesql.se