Package M.DN.PA and M.E.DM on *nix

Package M.DN.PA and M.E.DM on *nix

Build these packages on *nix, but don't publish them (they will not
have all of the content, since we don't yet build desktop versions of
the libraries when building on *nix).

As part of this work, I removed the GetBuildArgsByFrameworks task,
since we can just use conditional properties to remove the desktop
TFMs when we are building on *nix.

Fixes dotnet/core-setup#2319

Commit migrated from https://github.com/dotnet/core-setup/commit/f1033a8638aa62a252d8ea6efb24dcf287f3ce2a