Remove unnecessary RT attribute from LegacyDevOrder variable.

(Sync patch r16545 from main trunk.)

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ruiyu Ni <ruiyu.ni@intel.com>
Reviewed-by: Eric Dong <eric.dong@intel.com>

git-svn-id: https://svn.code.sf.net/p/edk2/code/branches/UDK2014.SP1@16546 6f19259b-4bc3-4df7-8a09-765794883524