tests: remove special handling for undefined memoryview
'memoryview' was introduced in Python 2.7. 4adc090fa2fb added code
to filterpyflakes.py to ignore "undefined name 'memoryview'" pyflakes
warnings. Since we no longer support <Python 2.7, we can remove this
workaround.
#require docutils gettext
$ $TESTDIR/check-gendoc zh_TW
checking for parse errors