pgsql: Fix misleading comment in nodeIndexonlyscan.c.

Fix misleading comment in nodeIndexonlyscan.c.

The stated reason for acquiring predicate locks on heap pages hasn't
existed since commit c01262a8, so fix the comment.  Perhaps in a later
release we'll also be able to change the code to use tuple locks.

Back-patch all the way.

Reviewed-by: Ashwin Agrawal
Discussion: https://postgr.es/m/CAEepm%3D2GK3FVdnt5V3d%2Bh9njWipCv_fNL%3DwjxyUhzsF%3D0PcbNg%40mail.gmail.com

Branch
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REL9_6_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/0908c5ecf0833b020b0d95183804ebc22bb6ea6c

Modified Files
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src/backend/executor/nodeIndexonlyscan.c | 7 ++-----
1 file changed, 2 insertions(+), 5 deletions(-)