Remove the now unused interlock argument to the lockmgr() procedure.

Remove the now unused interlock argument to the lockmgr() procedure.
This argument has been abused over the years by kernel programmers
attempting to optimize certain locking and data modification sequences,
resulting in a virtually unreadable code in some cases.  The interlock
also made porting between BSDs difficult as each BSD implemented their
interlock differently.  DragonFly has slowly removed use of the interlock
argument and we can now finally be rid of it entirely.