Have entity.remove() set active = false

Removes the need to check if an entity hasn't been removed prior to
processing.

core/src/com/me/asteroids/systems/CollisionSystem.java

@@ -23,7 +23,7 @@ public class CollisionSystem extends EntitySystem {
         Entity[] entities = getEntities().items;
         for (int i = 0, n = getEntities().size; i < n-1; i++) {
             Entity entityA = entities[i];
-            if (!entityA.isActive() || entityA.isRemoved()) {
+            if (!entityA.isActive()) {
                 continue;
             }
 
@@ -31,7 +31,7 @@ public class CollisionSystem extends EntitySystem {
 
             for (int j = i + 1; j < n; j++) {
                 Entity entityB = entities[j];
-                if (!entityB.isActive() || entityB.isRemoved()) {
+                if (!entityB.isActive()) {
                     continue;
                 }
 

core/src/com/me/common/ecs/Entity.java

@@ -50,6 +50,7 @@ public final class Entity {
 
     public void remove() {
         removed = true;
+        active = false;
         refresh();
     }
 

core/src/com/me/common/ecs/EntitySystem.java

@@ -29,7 +29,7 @@ public abstract class EntitySystem extends BaseSystem {
     public void process(float dt) {
         for (int i = 0, n = entities.size; i < n; i++) {
             Entity entity = entities.items[i];
-            if (!entity.removed && entity.active) {
+            if (entity.isActive()) {
                 processEntity(entity, dt);
             }
         }