python3-setuptools,python3-pip: Use more predictable pycache cleanup

python3-setuptools,python3-pip: Use more predictable pycache cleanup

This uses two find commands to delete __pycache__ contents then the
__pycache__ directories, rather than a for loop.

The second command omits a -empty test, so that if the first command
doesn't remove all directory contents for some reason, the second
command will return an error (find will not delete a non-empty
directory).

Signed-off-by: Jeffery To <jeffery.to@gmail.com>