refactor: a ContentLibrary must have a LearningPackage

[ormsbee]

Description

The learning_package of a ContentLibrary was originally made to be an
optional, nullable field for backwards compatibility. We were re-using
the same table when we transitioned from making v2 libraries be
Blockstore-based to making them Learning Core-based. Since that time,
Blockstore has been removed completely, and those prototype v2 libraries
are not functional anyway.

This commit removes those non-functional libraries and requires that all
new libraries going forward have a LearningPackage.

Note that this does not affect v1 legacy libraries that are backed by
Modulestore.

Implements #37443

[ormsbee]

Tested this locally on my machine:

mysql> select * from content_libraries_contentlibrary;
+----+-----------------+-----------------------+-------------------+--------+---------+---------------------+
| id | slug            | allow_public_learning | allow_public_read | org_id | license | learning_package_id |
+----+-----------------+-----------------------+-------------------+--------+---------+---------------------+
|  1 | PublishBehavior |                     0 |                 0 |      1 |         |                   1 |
|  2 | deletion-test   |                     0 |                 0 |      1 |         |                NULL |
|  3 | deletion-test2  |                     0 |                 0 |      1 |         |                NULL |
|  4 | deletion-test3  |                     0 |                 0 |      1 |         |                NULL |
+----+-----------------+-----------------------+-------------------+--------+---------+---------------------+
4 rows in set (0.00 sec)

mysql> select * from content_libraries_contentlibrary;
+----+-----------------+-----------------------+-------------------+--------+---------+---------------------+
| id | slug            | allow_public_learning | allow_public_read | org_id | license | learning_package_id |
+----+-----------------+-----------------------+-------------------+--------+---------+---------------------+
|  1 | PublishBehavior |                     0 |                 0 |      1 |         |                   1 |
+----+-----------------+-----------------------+-------------------+--------+---------+---------------------+
1 row in set (0.00 sec)

[ormsbee]

Hah, now it's running into LTI-launch tests that we never ripped out. 😞