devel/py-generate: Fix MASTER_SITES, Remove BROKEN [1]

While I'm here, address other ports bugs/issues [2]:

• gmake is not required (build uses distutils/setuptools:Extension)
• patch setup.py:version (was 2.2) to match PORTVERSION (2.8)
• Remove unecessary DISTNAME override
• Strip installed extension/library
• Correctly declare USES=python:<version-spec>, limited to 2.7. Fails to import on Python 3:
  
  ImportError: ... /site-packages/generate.so: Undefined symbol "PyString_FromString

PR: 241966
Submitted by: D'Arcy J.M. Cain <darcy druid net> [1]
Approved by: portmgr (blanket(s): ports compliance, dependencies) [2]
MFH: 2020Q1 (blanket(s): build (fetch) fix, ports compliance) [1][2]