maint(sympy): Remove deprecated imports

These names were importable before sympy 1.6 by accident. They were
replaced with deprecated import objects to give a warning in
sympy#19316

The warnings coming from these are now seen while building the docs and
are breaking the docs build in CI so this commit removes those names
meaning that they will have been giving a deprecation warning in sympy
1.6 and will be removed in sympy 1.7.