pgsql: Update .abi-compliance-history for pgstat_drop_entry()

Update .abi-compliance-history for pgstat_drop_entry()

As noted in the commit message of 850b9218c8e4, this function has gained
an extra called "missing_ok". All the callers of this routine should be
in core in the v15-v17 range. For v18, I have found one custom stats
kind that would be impacted by this change.

Discussion: /messages/by-id/ajOE3uRxVgSlPRcw@paquier.xyz
Backpatch-through: 15-18

Branch
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REL_18_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/8a4f389ddce54c5b9bc1f0dcc99e9f74944be813

Modified Files
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.abi-compliance-history | 9 +++++++++
1 file changed, 9 insertions(+)