graphics/py-sorl-thumbnail: Update to 12.6.3

• Assign to Django 2.2 (current LTS release) as Django 1.11 is End-of-Life.

• Make port concurrent safe as it installs files outside Python's site-lib directory.

• Separate USES block from non-relevant variables and pet portlint (whitespace issues in pkg-plist)

• Also remove an obsolete patch that was required to fix build issues with the documentation files.

Changelog:

https://github.com/jazzband/sorl-thumbnail/blob/12.6.3/CHANGES.rst

PR: 245358
Approved by: Kevin Golding <ports@caomhin.org> (maintainer)