chore: drop unused exports from modules QA harnesses load

QA harnesses import some modules in the page by path, for example
import('/src/data/radio.js'). Those calls name exactly which bindings
they use, and every other export of these modules has no importer:

- src/data/radio.js: 20 aliases of radio layer methods and two
  re-exported altitude constants. The radio layer keeps the methods.
- src/layers/transit/movement.js: tuning constants and course helpers
  used only inside the module lose `export`; FIX_HISTORY_MAX,
  DISPLAY_LAG_MIN_MS, DISPLAY_LAG_RESET_MS, FIX_NOISE_M, STOPPED_FIXES
  and courseBetween, which nothing reads, are deleted.
- src/overlays/worldOverlay.js, src/splitFlap.js,
  src/data/contactPlayback.js and src/voice/cloudVoiceAuth.js: helpers
  and constants used only locally lose `export`.

src/voice/cloudVoiceAuth.js

@@ -1,5 +1,5 @@
-export const CLOUD_VOICE_AUTH_MODES = Object.freeze(['api-key', 'oauth']);
-export const DEFAULT_CLOUD_VOICE_AUTH_MODE = 'api-key';
+const CLOUD_VOICE_AUTH_MODES = Object.freeze(['api-key', 'oauth']);
+const DEFAULT_CLOUD_VOICE_AUTH_MODE = 'api-key';
 export const CLOUD_VOICE_AUTH_STORAGE_KEY = 'godsEyeView.voice.cloudAuth';
 
 function storageRef(storage) {
@@ -11,7 +11,7 @@ function storageRef(storage) {
   }
 }
 
-export function normalizeCloudVoiceAuthMode(mode) {
+function normalizeCloudVoiceAuthMode(mode) {
   const normalized = String(mode || '')
     .trim()
     .toLowerCase();