refactor(api): remove schema

[ncclementi]

BREAKING CHANGE: Removed hierarchical usage of schema.

Ibis uses the following naming conventions:

• schema: a mapping of column names to datatypes
• database: a collection of tables
• catalog: a collection of databases

[github-actions]

ACTION NEEDED

Ibis follows the Conventional Commits specification for release automation.

The PR title and description are used as the merge commit message.

Please update your PR title and description to match the specification.

[ncclementi]

I'm not sure I understand how the test_signature.py works, because I clearly broke all of them, but is failing due to an XPASS, any help on that front would be appreciated.

[cpcloud]

If something is xpassing, generally the approach is to delete the marker that's causing the problem.

[gforsyth]

the signature check is to enforce (eventually) that all the backends call all positional arguments the same thing, etc (that's why currently, almost all of them are xfailed)

When you removed the schema kwarg, it made some of the backend-specific table methods match the method definition from BaseBackend.
also, keyword argument names also have to match, unless those arguments are keyword-only arguments

removing entries from those xfails is a good thing, though

[gforsyth]

Looks good overall, i think we lost one bit of testing that we shouldn't have.

[gforsyth]

Good riddance!

[gforsyth]

I've got to check to make sure the commit message is going to be formatted correctly, then we can merge