pgsql: Revert "Add recovery TAP test for race condition with slot inval

Revert "Add recovery TAP test for race condition with slot invalidations"

This reverts commit 08a52ab151ca, due to some sporadic instability in
the test.  Getting the test right should require some redesign with a
second injection point, but let's revert it for now to avoid these
issues in the CI as a lot of patches are under discussion in this last
commit fest.

Per buildfarm members hachi and gokiburi.

Discussion: https://postgr.es/m/ZekQQHCrIqLVpGz5@paquier.xyz

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/65db0cfb4c036b14520a22dba5a858185b713643

Modified Files
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src/backend/replication/slot.c                     |   9 --
.../recovery/t/035_standby_logical_decoding.pl     | 116 +--------------------
2 files changed, 2 insertions(+), 123 deletions(-)