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/overlays/worldOverlay.js

@@ -1155,11 +1155,7 @@ export function isOverlayPointVisible(
  * Return true when a rectangle intersects any cached UI exclusion box.
  * `count` lets pooled buffers expose a live prefix without truncating.
  */
-export function overlayRectIntersectsAny(
-  rect,
-  exclusions,
-  count = exclusions.length,
-) {
+function overlayRectIntersectsAny(rect, exclusions, count = exclusions.length) {
   for (let i = 0; i < count; i++) {
     const other = exclusions[i];
     if (
@@ -1177,7 +1173,7 @@ export function overlayRectIntersectsAny(
  * Like `overlayRectIntersectsAny`, but only against exclusions that composite
  * BELOW the host — the ones a placement may never overlap at any cost.
  */
-export function overlayRectIntersectsAnyHard(
+function overlayRectIntersectsAnyHard(
   rect,
   exclusions,
   count = exclusions.length,