Update Trove licence classifiers

[hugovk]

• The "Standard PIL license" has been identified as "Historical Permission Notice and Disclaimer (HPND)" (Review license #1507 (comment))
• This has now been added as a PyPI Trove classifier (Request Trove classifier: HPND licence pypi/warehouse#5627)

Changes proposed in this pull request:

• Sort the classifiers

• Replace License :: Other/Proprietary License with License :: OSI Approved :: Historical Permission Notice and Disclaimer (HPND)

• Remove the license parameter:

  • "this argument is meant for deviations from the Trove classifier, not instead of it" (Updated the "license" description to be more complete pypa/packaging.python.org#492)

[hugovk]

Pyroma was failing because "Your package does not have license data". When there's a known Trove licence, licence can and should be omitted, according to pypa/packaging.python.org#492.

I've reported this to pyroma (regebro/pyroma#38) and relaxed our test in the meantime.

[aclark4life]

LGTM, thanks