fix(core): fix bug where entity wasn't clearing properly

entity would still be on the add entity list as it hasn't been added yet so it would be added after it was removed

src/main/kotlin/com/noahbres/meepmeep/MeepMeep.kt

@@ -53,11 +53,11 @@ open class MeepMeep(private val windowSize: Int) {
     val windowFrame = WindowFrame("Meep Meep", windowSize)
     val canvas = windowFrame.canvas
 
-    protected var bg: Image? = null
+    private var bg: Image? = null
 
-    protected val colorManager = ColorManager()
+    private val colorManager = ColorManager()
 
-    protected val entityList = mutableListOf<Entity>()
+    private val entityList = mutableListOf<Entity>()
     private val requestedAddEntityList = mutableListOf<Entity>()
     private val requestedClearEntityList = mutableListOf<Entity>()
 
@@ -341,6 +341,7 @@ open class MeepMeep(private val windowSize: Int) {
 
     fun removeEntity(entity: Entity): MeepMeep {
         entityList.remove(entity)
+        requestedAddEntityList.remove(entity)
         entityListDirty = true