pgsql: Remove useless/superfluous Datum conversions

Remove useless/superfluous Datum conversions

Remove useless DatumGetFoo() and FooGetDatum() calls.  These are
places where no conversion from or to Datum was actually happening.

We think these extra calls covered here were harmless.  Some actual
bugs that were discovered during this process have been committed
separately (80c758a2e1d, 2242b26ce47).

Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://www.postgresql.org/message-id/flat/8246d7ff-f4b7-4363-913e-827dadfeb145%40eisentraut.org

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/dcfc0f891273eeeb85ce6e723decf5cc37f9b1c3

Modified Files
--------------
src/backend/commands/alter.c            | 2 +-
src/backend/executor/execExprInterp.c   | 6 +++---
src/backend/rewrite/rewriteDefine.c     | 5 ++---
src/backend/statistics/extended_stats.c | 2 +-
src/backend/tsearch/ts_parse.c          | 4 ++--
src/backend/utils/activity/pgstat.c     | 2 +-
src/backend/utils/adt/json.c            | 2 +-
src/backend/utils/adt/multirangetypes.c | 7 +++----
src/backend/utils/adt/rangetypes.c      | 4 ++--
src/backend/utils/adt/varlena.c         | 5 ++---
src/backend/utils/cache/relcache.c      | 2 +-
11 files changed, 19 insertions(+), 22 deletions(-)