Simplify newline handling in libpq TAP test

Simplify newline handling in libpq TAP test

CRLF translation is already handled by the text mode, so there should be
no need for any specific logic.  See also 1c6d4629394d, msys perl being
one case where the translation mattered.

Note: An equivalent has been first applied on HEAD with 8767b449a3a1.
The same change is backpatched to v18 as all the Windows buildfarm
members have reported green.

Author: Jacob Champion <jacob.champion@enterprisedb.com>
Co-authored-by: Michael Paquier <michael@paquier.xyz>
Reviewed-by: Daniel Gustafsson <daniel@yesql.se>
Discussion: https://postgr.es/m/aPsh39bxwYKvUlAf@paquier.xyz
Backpatch-through: 18