pgsql: Fix a leftover reference to backend_id in comment

Fix a leftover reference to backend_id in comment

Commit 024c521117 replaced backend_id with proc_number.

Reported-by: Alexander Lakhin

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/55cdba2647ed6bbe1126c6b6d8f53e8602ec05a1

Modified Files
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src/backend/utils/activity/backend_status.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)