Revert "Make .partial work with functools.partial objects"

This reverts commit 633ba4e4e37b94d3704c376177b146c16a9228f0.

The modification in 'test/test_decorator.py' is spared and stays.
Revert "Add partial support for functools.partial"

This reverts commit 7235143c2526aa943e29fc83418a18f9e4a157f4.

The modification in 'test/test_decorator.py' is spared and stays.
Simplify handling of functools.partial
Update tests for improved handling of functools.partial
Document conversion of functools.partial
Merge branch 'improve-partial-support'