pgsql: Update obsolete comment in ExecScanReScan().

Update obsolete comment in ExecScanReScan().

Commit 27cc7cd2b removed the epqScanDone flag from the EState struct,
and instead added an equivalent flag named relsubs_done to the EPQState
struct; but it failed to update this comment.

Author: Etsuro Fujita <etsuro.fujita@gmail.com>
Discussion: /messages/by-id/CAPmGK152zJ3fU5avDT5udfL0namrDeVfMTL3dxdOXw28SOrycg@mail.gmail.com
Backpatch-through: 13

Branch
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REL_18_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/233d79ec4fa09057e6707bd8da11758c4313f3cc

Modified Files
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src/backend/executor/execScan.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)