pgsql: Message improvement - Mailing list pgsql-committers

Message improvement

The previous wording contained a superfluous comma.  Adjust phrasing
for grammatical correctness and clarity.

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/0b5e8245283eef67e88fb5380836cdc2c743d848

Modified Files
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contrib/test_decoding/expected/slot.out        | 2 +-
src/backend/replication/logical/logicalfuncs.c | 2 +-
src/backend/replication/slotfuncs.c            | 2 +-
3 files changed, 3 insertions(+), 3 deletions(-)