pgsql: plpython: Remove support for major version conflict detection

plpython: Remove support for major version conflict detection

This essentially reverts commit 866566a690b, which installed
safeguards against loading plpython2 and plpython3 into the same
process. We don't support plpython2 anymore, so this is obsolete.

The Python and PL/Python initialization now happens again in
_PG_init() rather than the first time a PL/Python call handler is
invoked. (Often, these will be very close together.)

I kept the separate PLy_initialize() function introduced by
866566a690b to keep _PG_init() a bit modular.

Reviewed-by: Mario González Troncoso <gonzalemario(at)gmail(dot)com>
Reviewed-by: Nathan Bossart <nathandbossart(at)gmail(dot)com>
Discussion: https://www.postgresql.org/message-id/flat/9eb9feb6-1df3-4f0c-a0dc-9bcf35273111%40eisentraut.org

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/594ba21bce05e8682eaf024f705fea8aeaba5ef3

Modified Files
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src/pl/plpython/plpy_main.c | 65 +++------------------------------------------
1 file changed, 4 insertions(+), 61 deletions(-)