pgsql: Revert "Disable STARTUP_PROGRESS_TIMEOUT in standby mode."

Revert "Disable STARTUP_PROGRESS_TIMEOUT in standby mode."

This reverts commit 98e7234242a652497c99d4d0d6f2bf9a75d4e921. I
forgot that we're about to wrap a release, and this fix isn't
critical enough to justify committing it right before we wrap
a release.

Discussion: http://postgr.es/m/2676424.1675700113@sss.pgh.pa.us

Branch
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REL_15_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/1eadfbdd7eb0679ba8d45787aa8b2f06e76de20a

Modified Files
--------------
src/backend/access/transam/xlogrecovery.c | 25 +++----------------------
src/backend/postmaster/startup.c          | 30 +++---------------------------
src/include/postmaster/startup.h          |  2 --
3 files changed, 6 insertions(+), 51 deletions(-)