Remove 'screen' from screen identifier values - see #314

js/common/model/ScreenIdentifier.ts

@@ -5,6 +5,6 @@
  *
  * @author Sam Reid (PhET Interactive Simulations)
  */
-export const ScreenIdentifierValues = [ 'variabilityScreen', 'sourcesScreen', 'measuresScreen', 'samplingScreen' ] as const;
+export const ScreenIdentifierValues = [ 'variability', 'sources', 'measures', 'sampling' ] as const;
 
 export type ScreenIdentifier = typeof ScreenIdentifierValues[number];