pgsql: Remove no-longer-used parameter for create_groupingsets_path().

Remove no-longer-used parameter for create_groupingsets_path().

numGroups is unused since commit b5635948a; let's get rid of it.

XueJing Zhao, reviewed by Richard Guo

Discussion: https://postgr.es/m/DM6PR05MB64923CC8B63A2CAF3B2E5D47B7AD9@DM6PR05MB6492.namprd05.prod.outlook.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/f172b11d616e4e440be6b3235721e283e4c16460

Modified Files
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src/backend/optimizer/plan/planner.c  | 9 +++------
src/backend/optimizer/util/pathnode.c | 4 +---
src/include/optimizer/pathnode.h      | 3 +--
3 files changed, 5 insertions(+), 11 deletions(-)