Remove some dead code.

Fixes CID #965946.
Improve the Get(Cur)DispMode and SetDispMode functions.

Fixes CID #966222.
Update LAV Filters to 0.58.2-95-f326e37 (custom build based on 0.58.2-90-602b085).

Important change: Fix a crash when opening RealMedia streaming (ticket #3342).