pgsql: Back off chattiness in RemovePgTempFiles().

Back off chattiness in RemovePgTempFiles().

In commit 561885db0, as part of normalizing RemovePgTempFiles's error
handling, I removed its behavior of silently ignoring ENOENT failures
during directory opens. Thomas Munro points out that this is a bad idea at
the top level, because we don't create pgsql_tmp directories until needed.
Thus this coding could produce LOG messages in perfectly normal situations,
which isn't what I intended. Restore the suppression of ENOENT logging,
but only at top level --- it would still be unexpected for a nested temp
directory to disappear between seeing it in the parent directory and
opening it.

Discussion: https://postgr.es/m/CAEepm=2y06SehAkTnd5sU_eVqdv5P-=Srt1y5vYNQk6yVDVaPw@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/eeb3c2df429c943b2f8d028d110b55ac0a53dc75

Modified Files
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src/backend/storage/file/fd.c | 28 ++++++++++++++++++++--------
1 file changed, 20 insertions(+), 8 deletions(-)