function removeClouds(cloudCollection) {
  if (cloudCollection._cloudsRemoved) {
    cloudCollection._cloudsRemoved = false;

    const newClouds = [];
    const clouds = cloudCollection._clouds;
    const length = clouds.length;
    for (let i = 0, j = 0; i < length; ++i) {
      const cloud = clouds[i];
      if (defined(cloud)) {
        clouds._index = j++;
        newClouds.push(cloud);
      }
    }

    cloudCollection._clouds = newClouds;
  }
}
Removes all clouds from the collection.

@performance <code>O(n)</code>.  It is more efficient to remove all the clouds
from a collection and then add new ones than to create a new collection entirely.

@exception {DeveloperError} This object was destroyed, i.e., destroy() was called.

@example
clouds.add(...);
clouds.add(...);
clouds.removeAll();

@see CloudCollection#add
@see CloudCollection#remove