pgsql: Revert 019_replslot_limit.pl related debugging aids.

Revert 019_replslot_limit.pl related debugging aids.

This reverts most of 91c0570a791, f28bf667f60, fe0972ee5e6, afdeff10526. The
only thing left is the retry loop in 019_replslot_limit.pl that avoids
spurious failures by retrying a couple times.

We haven't seen any hard evidence that this is caused by anything but slow
process shutdown. We did not find any cases where walsenders did not vanish
after waiting for longer. Therefore there's no reason for this debugging code
to remain.

Discussion: https://postgr.es/m/20220530190155.47wr3x2prdwyciah@alap3.anarazel.de
Backpatch: 15-

Branch
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REL_15_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/49ddd98763624cfb6020f8b525a021e9788473a5

Modified Files
--------------
src/backend/replication/slot.c | 43 -------------------------------
src/backend/storage/lmgr/lwlock.c | 7 -----
src/backend/utils/init/postinit.c | 18 -------------
src/bin/pg_basebackup/pg_basebackup.c | 10 +------
src/include/storage/lwlock.h | 1 -
src/test/recovery/t/019_replslot_limit.pl | 13 +++-------
6 files changed, 5 insertions(+), 87 deletions(-)