pgsql: Remove unnecessary members from ModifyTableState and ExecInsert

Remove unnecessary members from ModifyTableState and ExecInsert

These values can be obtained from the ModifyTable node which is already
a part of both the ModifyTableState and ExecInsert.

Author: Álvaro Herrera, Amit Langote
Reviewed-by: Peter Geoghegan
Discussion: https://postgr.es/m/20180316151303.rml2p5wffn3o6qy6@alvherre.pgsql

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/ee0a1fc84eb29c916687dc5bd26909401d3aa8cd

Modified Files
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src/backend/executor/execPartition.c   |  4 ++--
src/backend/executor/nodeModifyTable.c | 34 +++++++++++++++++++---------------
src/include/nodes/execnodes.h          |  3 ---
3 files changed, 21 insertions(+), 20 deletions(-)