UnixPkg: Remove UnixPkg files (It is replaced by EmulatorPkg)

For now the UnixPkg/Deprecated.txt file is retained to indicate
that EmulatorPkg should be used instead.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>

git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@14518 6f19259b-4bc3-4df7-8a09-765794883524