deregister the same method we registered

[chriselion]

Currently we add one method in OnEnableHelper() but remove another in OnDisable()

ml-agents/UnitySDK/Assets/ML-Agents/Scripts/Agent.cs

Lines 280 to 300 in 1a240bb

	academy.AgentForceReset += _AgentReset;
	m_PolicyFactory = GetComponent<BehaviorParameters>();
	m_Brain = m_PolicyFactory.GeneratePolicy(Heuristic);
	ResetData();
	InitializeAgent();
	InitializeSensors();
	}
	/// Monobehavior function that is called when the attached GameObject
	/// becomes disabled or inactive.
	void OnDisable()
	{
	var academy = FindObjectOfType<Academy>();
	if (academy != null)
	{
	academy.AgentSetStatus -= SetStatus;
	academy.AgentResetIfDone -= ResetIfDone;
	academy.AgentSendState -= SendInfo;
	academy.DecideAction -= DecideAction;
	academy.AgentAct -= AgentStep;
	academy.AgentForceReset -= ForceReset;

The original intent was probably to add ForceReset(), but to keep behavior consistent, we'll remove _AgentReset() instead