Revert "[Core] Document all exported core methods with type hints"

Typing is broken with older versions of Twisted e.g. with v21.2

    deluge/deluge/core/core.py", line 404, in Core
        ) -> defer.Deferred[str]:
    TypeError: 'type' object is not subscriptable

Also it might not be compatible with Python 3.6 or 3.7 with use of
certain types such as dict rather than Dict

This reverts commit 4096cdf.

Ref: https://twistedmatrix.com/trac/ticket/9816