pgsql: Fix misuse of foreach_delete_current().

Fix misuse of foreach_delete_current().

Our coding convention requires this macro's result to be assigned
back to the original List variable.  In this usage, since the
List could not become empty, there was no actual bug --- but
some compilers warned about it.  Oversight in be45be9c3.

Discussion: https://postgr.es/m/35077b31-2d62-1e31-0e2e-ddb52d590b73@enterprisedb.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/1d581ce7129d7a33cd4ad27f8f246abfa1fd2db9

Modified Files
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src/backend/parser/parse_agg.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)