textproc/py-textfsm: Switch back to PyPI

• During QA tests of net-mgmt/py-napalm, runtime errors occured because the egg-info of py-textfsm still had version information of the prior release (= 1.1.2).
  
  This was because when version 1.1.3 was released, it was already available in the upstream repository, but there was no sdist available at PyPI yet. This was then made up by upstream some months later with a corresponding adjustment for the egg-info:
  
  https://github.com/google/textfsm/compare/v1.1.3...ca3755dc
  
  Therefore, switch back to PyPI, which is the preferred method with respect to Python ports and bump PORTREVISION due package change.

While I'm here:

• Re-evaluate and remove no longer required BUILD_DEPENDS.
• Simplify Makefile by switching to USE_PYTHON=pytest.

MFH: 2023Q2