Revert "adbd: switch to su domain when running as root"

This reverts commit c52c5b8e3d690201b2ae009a2d396d1899033e3d.

 * This breaks the adb recovery banner, and root_seclabel is not
   a valid option on cm11.

Change-Id: I0dede5d38b53b00936ad901e61d65f6119e62ff5