Move entityclass::setenemy() to entclass::setenemy()

This moves the setenemy() function onto the entity object itself,
instead of having to give the indice of the entity in obj.entities. This
makes the code more object-oriented so later I can simply change all
'entities[k]' to 'entity.' in entityclass::createentity().

desktop_version/src/Entity.h

@@ -84,8 +84,6 @@ public:
 
     void setenemyroom(int t, int rx, int ry);
 
-    void setenemy(int t, int r);
-
     void settreadmillcolour(int t, int rx, int ry);
 
     void createentity(float xp, float yp, int t, float vx = 0, float vy = 0,