Remove `litestar.contrib` namespace

The litestar.contrib module has been deprecated and will be removed in version 3, the functionality has been moved to litestar.plugins. All litestar.contrib submodules need to be removed. This is going to happen in individual PRs, and I've created a corresponding sub-issue down below.

• Delete the litestar.contrib.<namespace> module
• Remove tests for the deprecation warnings for importing litestar.contrib.<namespace>
• If there is documentation in docs/usage referencing the removed module, update it to the new litestar.plugins.<namespace> references
• If there is a file docs/reference/contrib/<namespace.rst>, delete it. If no corresponding file in docs/reference/plugins/<namespace>.rst exists, move the file there instead of deleting it
• Add an entry in docs/release-notes/changelog.rst (use the outline below)
• Create a PR with an appropriate title and breaking (!) indicator, e.g. feat(jwt)!: remove depreacated 'litestar.contrib.jwt' module

Changelog entry template:

.. change:: Remove deprecated ``litestar.contrib.<namespace>`` module
    :type: feature
    :breaking:
    :pr: <pr number>
    :issue: <issue number>
    
    Remove the deprecated ``litestar.contrib.<namespace>`` module. Code still using imports 
    from this module should switch to using ``litestar.plugins.<namespace>``.

    .. place special migration instructions / considerations here if necessary