message: Remove deprecated code from StyleSetEvalutator.
  Remove filtering state bookkeeping that became obsolete after removal of
  nested styles
diff: @@ -353,32 +353,18 @@ export class StyleSetEvaluator {
  optimizedSubSetKey.set(layer, geometryType, env);
  // get the requested $layer and $geometryType, if any.
  - const currentLayer = optimizedSubSetKey.layer;
  - const currentGeometryType = optimizedSubSetKey.geometryType;
  + this.m_layer = optimizedSubSetKey.layer;
  + this.m_geometryType = optimizedSubSetKey.geometryType;
  + this.m_zoomLevel = env.lookup("$zoom") as number | undefined;
  const searchedStyleSet = this.getOptimizedStyleSet(optimizedSubSetKey);
  - const previousZoomLevel = this.changeZoomLevel(env.lookup("$zoom") as number | undefined);
  -
  - // set the requested $layer as the current layer.
  - const previousLayer = this.changeLayer(
  - typeof currentLayer === "string" ? currentLayer : undefined
  - );
  -
  - const previousGeometryType = this.changeGeometryType(
  - typeof currentGeometryType === "string" ? currentGeometryType : undefined
  - );
  -
  for (const currStyle of searchedStyleSet) {
  if (this.processStyle(env, currStyle, result)) {
  break;
  }
  }
  - this.changeLayer(previousLayer); // restore the layer
  - this.changeGeometryType(previousGeometryType); // restore the geometryType
  - this.changeZoomLevel(previousZoomLevel);
  -
  return result;
  }
  @@ -429,24 +415,6 @@ export class StyleSetEvaluator {
  return this.m_techniques.map(makeDecodedTechnique);
  }
  - private changeLayer(layer: string | undefined) {
  - const savedLayer = this.m_layer;
  - this.m_layer = layer;
  - return savedLayer;
  - }
  -
  - private changeGeometryType(geometryType: string | undefined) {
  - const savedGeometryType = this.m_geometryType;
  - this.m_geometryType = geometryType;
  - return savedGeometryType;
  - }
  -
  - private changeZoomLevel(zoomLevel: number | undefined) {
  - const savedZoomLevel = this.m_zoomLevel;
  - this.m_zoomLevel = zoomLevel;
  - return savedZoomLevel;
  - }
  -
  private getOptimizedStyleSet(subSetKey: OptimizedSubSetKey): InternalStyle[] {
  if (subSetKey.cachedStyleSet !== undefined) {
  return subSetKey.cachedStyleSet;
  @@ -597,16 +565,22 @@ export class StyleSetEvaluator {
  return style.final === true;
  }
  - private checkZoomLevel(env: Env, style: InternalStyle): boolean {
  + private checkZoomLevel(env: Env, style: InternalStyle) {
  + if (style.minZoomLevel === undefined && style.maxZoomLevel === undefined) {
  + return true;
  + }
  +
  const zoomLevel = this.m_zoomLevel;
  + if (zoomLevel === undefined) {
  + return true;
  + }
  - if (zoomLevel !== undefined) {
  if (style.minZoomLevel !== undefined) {
  let minZoomLevel: Value = style.minZoomLevel;
  if (style._minZoomLevelExpr) {
  // the constraint is defined as expression, evaluate it and
  - // use its vlaue
  + // use its value
  try {
  minZoomLevel = style._minZoomLevelExpr.evaluate(
  env,
  @@ -650,7 +624,6 @@ export class StyleSetEvaluator {
  return false;
  }
  }
  - }
  return true;
  }
  