ManageabilityPkg: reorganise ManageabilityTransportSsifLib

For some reason this module was created "backwards", with .inf files
in subdirectories, as well as identical apart from failes to keep in
sync source files for Dxe and Pei drivers.

Flip the thing the right way around and delete the duplicated files.

Signed-off-by: Leif Lindholm <leif.lindholm@oss.qualcomm.com>