media-fonts/liberation-fonts: Fix python-any-r1 usage

media-fonts/liberation-fonts: Fix python-any-r1 usage

Non-maintainer commit.

The usage of python-any-r1 was incomplete.  This commit fixes:

* Adding python_gen_any_dep so valid USE are connected to python deps
* Adding python_check_deps to validate if a dep is actually installed
* sed the Makefile to use EPYTHON for consistent builds instead of user pref
* Changing DEPEND to BDEPEND on EAPI7 as they are tools run by the build

Closes: https://bugs.gentoo.org/698128
Package-Manager: Portage-2.3.81, Repoman-2.3.20
Signed-off-by: Brian Evans <grknight@gentoo.org>