tree shaking doesn't get rid of dead hex literal

[tballmsft]

• see https://makecode.microbit.org/_fY9cVRgEp1VD and the compiler error on download
• the variable rocketJourney in animations.ts (let clause) is not used anywhere in the code.
• if you comment out this line, the project builds.
• if you uncomment the line, the project fails

The same problem occurs if you replace "let" with "const" in animations.ts

[mmoskal]

isSideEffectfulInitializer in emitter.ts seems wrong; will fix