eselect python: drop usage

Now that we have newer versions of python-exec, we no longer need to
call eselect python at all.  Control over which versions of Python
are used is determined entirely by python-exec now via USE flags.

BUG=b:187794810
TEST=CQ passes

Change-Id: Ie54898f3c93cb49b767f9bf2b1cc3f2881008a6d
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosutils/+/3633065
Tested-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Sergey Frolov <sfrolov@google.com>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
3 files changed