pgsql: Correct _bt_delitems_vacuum() lock comments.

Correct _bt_delitems_vacuum() lock comments.

The expectation within _bt_delitems_vacuum() is that caller has a
super-exclusive/cleanup buffer lock (not just a pin and a write lock).

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/44e44bd258a71162444d41a1044c795f2c6dd3d1

Modified Files
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src/backend/access/nbtree/nbtpage.c | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)