dev-python/pyenchant: bump to 2.0.0, supports enchant 2, Py3.7+PyPy3

dev-python/pyenchant: bump to 2.0.0, supports enchant 2, Py3.7+PyPy3

* This new version works with enchant v1.x and v2.x so we can get rid of
  ${PV%.*} in RDEPEND.
* app-dicts/myspell-en must be installed to avoid the failure from bug 659258.
* Tests are fine as long as a UTF-8 locale is present, not necessarily
  en_US.UTF-8, remove the locale check from python_test.
* When using a non-English locale, one test might fail, so it's
  commented out and the failure is reported upstream.

Closes: https://bugs.gentoo.org/643718
Closes: https://bugs.gentoo.org/659258
Closes: https://bugs.gentoo.org/656172
Package-Manager: Portage-2.3.43, Repoman-2.3.10