pgsql: Remove an obsolete comment in gistinsert()

Remove an obsolete comment in gistinsert()

This is inconsistent since 1f7ef548ec2e where the definition of
gistFormTuple() has changed.

Author: Tender Wang
Reviewed-by: Aleksander Alekseev
Discussion: https://postgr.es/m/CAHewXNkjU95_HdioDVU=5yBq_Xt=GfBv=Od-0oKtiA006pWW7Q@mail.gmail.com

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/987027bcc04397f963bb961092a83067c0e406bb

Modified Files
--------------
src/backend/access/gist/gist.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)