This reverts commit 8d7c38b8.

Reason: Lot of the additions aren't adding value.

[ci skip]

Now that migrations support instance methods, we should
use the same instance rather than relying on delegation
to a global instance. This allows subclassing AR::Schema.

an alias is provided.  Without the alias, the column cannot be found
and properly typecast.

Rename test file so that the test suite matches it, implement `persisted?` for SqlBypass as expected by tests and convert session_id to string before using on queries to get correct quotes on postgresql (avoid casting error).

Remove unnecessary assertions. We should only test the before_seq isn't same to the after_seq when using sequencer.

This reverts commit 3b6c0e35.

Reason: changelogs aren't meant to be edited in docrails.

Introduced in 7ecfe3d3