www/py-grequests: Update to 0.3.0, Modernize

• Update PORTVERSION and distinfo checksum (0.3.0)
• Update TEST_DEPENDS and test target to new framework
• Remove TESTS option bits accordingly
• Enable NO_ARCH (Architecture independent)
• Remove unnecessary setup.py patch (upstreamed)
• Remove patch for test_grequests.py (backport)
• Backport patch for removing failing test [1]

[1] https://github.com/kennethreitz/grequests/pull/83