Remove unused function entityclass::changecustomcollect()

Looks like all accesses on obj.customcollect are done manually, so this
function is unused.

desktop_version/src/Entity.cpp

@@ -94,11 +94,6 @@ void entityclass::confirmflags()
     }
 }
 
-void entityclass::changecustomcollect( int t, int s )
-{
-    collect[t] = s;
-}
-
 int entityclass::swncolour( int t )
 {
     //given colour t, return colour in setcol