[metadata/layout.conf] Whitespace.
[metadata/layout.conf] Set profile-layouts.
[profiles/package.mask] Make package.mask a directory.

This allows us to avoid having to manually run regenerate-files
for every change.
[Documentation] Stop generating package.mask

Since we set profile-formats = portage, we can use package.mask
as a directory so we don't need to regenerate it every time.
[profiles/package.mask] Remove obsolete mask.
[profiles/package.mask] Update mask message and remove package that no longer needs to be masked.

extra-cmake-modules doesn't have cross-overlay dependencies
so does not need to be unmasked since it is now released.