Remove the galgebra.deprecated module

[utensil]

Mark the work that would be left by #286, see tasks in https://github.com/pygae/galgebra/pull/286#issuecomment-623850152:

Before we actually remove them, we need to ensure we have equivalent tests outside Old Format, it provided a significant coverage boost.

The approach could be:

1. Start by moving theses classes out of GAlgebra to test as merely a test facility
2. Remove the duplicated tests in Old Format; (because @abrombo had already ported many to the new format)
3. Port the tests the increases coverage to the new format.