Since we're checking `serializable?` in the new `HomogeneousIn`
`serialize` will no longer raise an exception. We implemented
`unchecked_serialize` to avoid raising in these cases, but with some of
our refactoring we no longer need it.

I discovered this while trying to fix a query in our application that
was not properly serializing binary columns. I discovered that in at
least 2 of our active model types we were not calling the correct
serialization. Since `serialize` wasn't aliased to `unchecked_serialize`
in `ActiveModel::Type::Binary` and `ActiveModel::Type::Boolean` (I
didn't check others but pretty sure all the AM Types are broken) the SQL
was being treated as a `String` and not the correct type.

This caused Rails to incorrectly query by string values. This is
problematic for columns storing binary data like our emoji columns at
GitHub. The test added here is an example of how the Binary type was
broken previously. The SQL should be using the hex values, not the
string value of "🥦" or other emoji.

We still have the problem `unchecked_serialize` was supposed to fix -
that `serialize` shouldn't validate data, just convert it. We'll be
fixing that in a followup PR so for now we should use `serialize` so we
know all the values are going through the right serialization for their
SQL.