pgsql: Revert "graceful shutdown" changes for Windows, in back branches

Revert "graceful shutdown" changes for Windows, in back branches only.

This reverts commits 6051857fc and ed52c3707, but only in the back
branches. Further testing has shown that while those changes do fix
some things, they also break others; in particular, it looks like
walreceivers fail to detect walsender-initiated connection close
reliably if the walsender shuts down this way. We'll keep trying to
improve matters in HEAD, but it now seems unwise to push these changes
into stable releases.

Discussion: https://postgr.es/m/CA+hUKG+OeoETZQ=Qw5Ub5h3tmwQhBmDA=nuNO3KG=zWfUypFAw@mail.gmail.com

Branch
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REL_10_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/645c9457f296bdd674b3efc37047194db8233e66

Modified Files
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src/backend/libpq/pqcomm.c | 29 +++++++----------------------
1 file changed, 7 insertions(+), 22 deletions(-)