pgsql: Remove useless assertions

Remove useless assertions

We don't need Assert(IsA(foo, String)) right before running
strVal(foo), since strVal() already does the assertion internally (via
castNode()).

Branch
------
master

Details
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https://git.postgresql.org/pg/commitdiff/503e3833ef240c94e114be8703046d52f24da021

Modified Files
--------------
src/backend/commands/tablecmds.c |  2 --
src/backend/commands/typecmds.c  |  1 -
src/backend/executor/functions.c |  2 --
src/backend/parser/parse_expr.c  | 10 ----------
src/pl/plpgsql/src/pl_comp.c     |  6 ------
5 files changed, 21 deletions(-)