Unity animation events or AnimationUtility API does not contain methods for deleting animation clip events at runtime. The following code makes it possible.

RemoveEventFromAnimator.cs

    /// <summary>
    /// Unity animation events or AnimationUtility API does not contain methods for deleting animation clip events at runtime.The following code makes it possible.
    /// Taken from (with a minor bug fix): https://forum.unity.com/threads/remove-animation-event.78957/
    /// </summary>
     
     public static void RemoveEventFromAnimator(string functionName, Animator animator)
     {
         AnimatorClipInfo animationClipInfo = animator.GetCurrentAnimatorClipInfo(0)[0];
         AnimationClip animationClip = animationClipInfo.clip;
 
         AnimationEvent[] animationEvents = animationClip.events;
         List<AnimationEvent> updatedAnimationEvents = new List<AnimationEvent>();
 
         for (int i = 0; i < animationEvents.Length; i++)
         {
             AnimationEvent animationEvent = animationEvents[i];
             if (animationEvent.functionName != functionName)
             {
                 updatedAnimationEvents.Add(animationEvent);
             }
         }
 
         animationClip.events = updatedAnimationEvents.ToArray();
     }