pg_upgrade from 12 to 13 failes with plpython2

[Marcin Giedz <marcin.giedz@xxxxxxxx>]

Hi all, trying to performe upgrade from 12 to 13 installed from Centos8 repo gives such error:

cat loadable_libraries.txt
could not load library "$libdir/plpython2": ERROR:  could not access file "$libdir/plpython2": No such file or directory

digging around:

1.

drop extension plpythonu;
ERROR:  extension "plpythonu" does not exist

2.

postgres=# select * from pg_pltemplate ;
  tmplname  | tmpltrusted | tmpldbacreate |      tmplhandler       |        tmplinline        |    tmplvalidator    |    tmpllibrary    | tmplacl
------------+-------------+---------------+------------------------+--------------------------+---------------------+-------------------+---------
 plpgsql    | t           | t             | plpgsql_call_handler   | plpgsql_inline_handler   | plpgsql_validator   | $libdir/plpgsql   |
 pltcl      | t           | t             | pltcl_call_handler     |                          |                     | $libdir/pltcl     |
 pltclu     | f           | f             | pltclu_call_handler    |                          |                     | $libdir/pltcl     |
 plperl     | t           | t             | plperl_call_handler    | plperl_inline_handler    | plperl_validator    | $libdir/plperl    |
 plperlu    | f           | f             | plperlu_call_handler   | plperlu_inline_handler   | plperlu_validator   | $libdir/plperl    |
 plpythonu  | f           | f             | plpython_call_handler  | plpython_inline_handler  | plpython_validator  | $libdir/plpython2 |
 plpython2u | f           | f             | plpython2_call_handler | plpython2_inline_handler | plpython2_validator | $libdir/plpython2 |
 plpython3u | f           | f             | plpython3_call_handler | plpython3_inline_handler | plpython3_validator | $libdir/plpython3 |
(8 rows)

3.

postgres=# select * from pg_language ;
  oid  | lanname  | lanowner | lanispl | lanpltrusted | lanplcallfoid | laninline | lanvalidator | lanacl
-------+----------+----------+---------+--------------+---------------+-----------+--------------+--------
    12 | internal |       10 | f       | f            |             0 |         0 |         2246 |
    13 | c        |       10 | f       | f            |             0 |         0 |         2247 |
    14 | sql      |       10 | f       | t            |             0 |         0 |         2248 |
 14177 | plpgsql  |       10 | t       | t            |         14174 |     14175 |        14176 |
(4 rows)

4.

postgres=# select  DISTINCT l.lanname as function_language
postgres-# from pg_proc p
postgres-# left join pg_language l on p.prolang = l.oid;
 function_language
-------------------
 c
 sql
 internal
(3 rows)

5.

postgres=# SELECT oid::regprocedure
postgres-# FROM pg_catalog.pg_proc
postgres-# WHERE probin = '$libdir/plpython2';
 oid
-----
(0 rows)

Question: where is plpython2 comming from during pg_upgrade? Is this pg_upgrade bug or something else?

Thx

Marcin