www/py-aiohttp: Update to 3.5.4

• Drop use of cython, only needed for 'from git' builds
• Document necessary but not-yet-ported TEST_DEPENDS for our future selves and potential contributors to see.
• Update port metadata to match upstream: pkg-desc, WWW URL, LICENSE, COMMENT
• Patch setup.py: Add necessary but missing entries to tests_require. For the ones not yet ported, they're fetched from PyPI via setuptools when correctly declared. Move pytest min version requirement from pytest.ini to tests_require where it belongs, so it can be parsed and the right version can be fetched, instead of just failing if its not the required version.
• Patch pytest.ini: Strip --cov from pytest args. We don't care about coverage downstream, and it shouldnt be a compulsory (tests_require) dependency, but instead an extras_require, so dont add it to TEST_DEPENDS even though it is a port.

Changelog:

https://github.com/aio-libs/aiohttp/blob/v3.5.4/CHANGES.rst

PR: 228575