001_ssltests.pl and 002_scram.pl both generated an extra file for a
client key used in the tests that were not removed.  In Debian, this
causes repeated builds to fail.

The code refactoring done in 4dc63552 broke the cleanup done in
001_ssltests.pl, and the new tests added in 002_scram.pl via d6e612f8
forgot the removal of one file.  While on it, fix a second issue
introduced in 002_scram.pl where we use the same file name in 001 and
002 for the temporary client key whose permissions are changed in the
test, as using the same file name in both tests could cause failures
with parallel jobs of src/test/ssl/ if one test removes a file still
needed by the second test.

Reported-by: Felix Lechner
Author: Daniel Gustafsson, Felix Lechner
Reviewed-by: Tom Lane, Michael Paquier
Discussion: https://postgr.es/m/CAFHYt543sjX=Cm_aEeoejStyP47C+Y3+Wh6WbirLXsgUMaw7iw@mail.gmail.com
Backpatch-through: 13