Remove unused function entityclass::changecustomcollect()

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

desktop_version/src/Entity.h

@@ -32,8 +32,6 @@ public:
 
     void confirmflags();
 
-    void changecustomcollect(int t, int s);
-
     void fatal_top()
     {
         createblock(DAMAGE, -8, -8, 384, 16);