textproc/py-tablib: Fix RUN_DEPENDS of devel/py-backports.csv

• The Python version restriction of devel/py-backports.csv was relaxed in r519566. Thus update the RUN_DEPENDS accordingly and remove the workaround for setup.py which is no longer needed.

• Bump PORTREVISION for package change.

PR: 243339
Submitted by: sunpoet
MFH: 2020Q1 (blanket: fix of runtime dependencies)