pgsql: plpython: Code cleanup related to removal of Python 2 support.

plpython: Code cleanup related to removal of Python 2 support.

Since 19252e8ec93 we reject Python 2 during build configuration. Now that the
dust on the buildfarm has settled, remove Python 2 specific code, including
the "Python 2/3 porting layer".

The code to detect conflicts between plpython using Python 2 and 3 is not
removed, in case somebody creates an out-of-tree version adding back support
for Python 2.

Reviewed-By: Peter Eisentraut <peter@eisentraut.org>
Reviewed-By: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/20211031184548.g4sxfe47n2kyi55r@alap3.anarazel.de

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/9b7e24a2cb37fb52af13219f625cd719e364a346

Modified Files
--------------
contrib/hstore_plpython/hstore_plpython.c | 12 +++----
contrib/jsonb_plpython/jsonb_plpython.c   | 27 ++++++--------
contrib/ltree_plpython/ltree_plpython.c   |  6 +---
src/pl/plpython/plpy_cursorobject.c       |  8 ++---
src/pl/plpython/plpy_elog.c               | 26 ++++++--------
src/pl/plpython/plpy_exec.c               | 44 +++++++++++------------
src/pl/plpython/plpy_main.c               | 59 ++++++-------------------------
src/pl/plpython/plpy_planobject.c         |  2 +-
src/pl/plpython/plpy_plpymodule.c         | 32 +++++------------
src/pl/plpython/plpy_plpymodule.h         |  2 --
src/pl/plpython/plpy_resultobject.c       | 16 +++------
src/pl/plpython/plpy_spi.c                | 10 +++---
src/pl/plpython/plpy_typeio.c             | 40 +++++++++------------
src/pl/plpython/plpy_util.c               |  9 -----
src/pl/plpython/plpy_util.h               |  2 --
src/pl/plpython/plpython.h                | 34 +-----------------
16 files changed, 95 insertions(+), 234 deletions(-)