Remove arbitrary bitmap size limit
Remove arbitrary bitmap size limit

We're not aware of any specific reason for this number to be used,
and actual potentially-dangerous cases should be handled by the
other limits.

Fixes #260

astiob/libass,Akemi/libass,Akemi/libass,MrSmile/libass,MrSmile/libass,xbmc/libass,libass/libass,Akemi/libass,ShiftMediaProject/libass,astiob/libass,libass/libass,xbmc/libass,ShiftMediaProject/libass