This change makes the respective operations work with non-`TensorVariable` classes.

This removes some unused steps involving a missing `SymbolicInputKits` and
changes `FunctionMaker._check_unused_inputs` to a static method without the
preceding underscore.

This prevents low-level errors recently introduced by newer versions of
`jaxlib`.

The new SciPy release has a restructured `scipy.signal` namespace
and some imports in Aesara need to be refactored accordingly.
This will most probably increase the lower limit on the SciPy version.

See tracking issue #810.

Bug was introduced in b920bd29

Closes #709