[Proposal] [Small] Remove unnecessary design

[chrisgervang]

• Remove "active features" from keyframes. Doesn't add value, increases maintenance overhead.
  

  hubble.gl/modules/core/src/keyframes/keyframes.js

  Lines 87 to 97 in abe5c30

  	_setActiveFeatures(keyframes) {
  	const firstKeyframe = keyframes[0];
  	this.activeFeatures = Object.keys(firstKeyframe).reduce((activeFeatures, key) => {
  	// activate only keys that are expected
  	if (firstKeyframe[key] !== undefined) {
  	activeFeatures[key] = true;
  	}
  	return activeFeatures;
  	}, this.activeFeatures);
  	}
  	}

• Remove "animator" function from Animation classes. Use existing "draw" function in sub-classes instead, and decrease maintenance overhead.
  

  hubble.gl/modules/core/src/animations/deck-animation.js

  Line 91 in abe5c30

  animator(animation) {

  
  

  hubble.gl/modules/core/src/animations/kepler-animation.js

  Line 162 in abe5c30

  animator(animation) {

  
  

  hubble.gl/modules/core/src/animations/animation.js

  Line 39 in abe5c30

  attachAnimator(animator) {