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_15_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/1cba25e4cf2ea0d8efd1d3c8d0af3f7a3c091dfe

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