[conf/noarch] drop VCS dependencies from app-portage/layman

With layman 2.2.0, USE flags need to be enabled to have support for
an overlay using particular VCS, but we don't want layman to depend on
the VCSes. Layman still handles a missing VCS gracefully as indicated
on bug 4822, comment 7.
Revert "Revert "[intel/portage] app-portage/layman: bazaar git mercurial subversion""

This reverts commit 4f10534bd1b30b8ee423e62ea2478f4524da40b6.

** I'm on it, just pushed too quickly! **