Parser cleanup.

src/backend/executor/execUtils.c

src/backend/nodes/copyfuncs.c

src/backend/nodes/outfuncs.c

src/backend/nodes/print.c

src/backend/nodes/readfuncs.c

src/backend/parser/analyze.c

src/backend/parser/gram.y

src/backend/parser/keywords.c

src/backend/parser/parse_agg.c

src/backend/parser/parse_clause.c

src/backend/parser/parse_expr.c

src/backend/parser/parse_func.c

src/backend/parser/parse_node.c

src/backend/parser/parse_oper.c

src/backend/parser/parse_relation.c

src/backend/parser/parse_target.c

src/backend/utils/cache/lsyscache.c

src/include/parser/parse_agg.h

src/include/parser/parse_expr.h

src/include/parser/parse_func.h