staging: r8188eu: Remove - number of dummy and unused routines

These routines include:
ODM_StartWorkItem()
ODM_StopWorkItem()
ODM_FreeWorkItem()
ODM_ScheduleWorkItem()
ODM_IsWorkItemScheduled()

Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>