revert(eink): drop full refresh on screen change — too much black-flash

A full (non-partial) refresh on every screen change (638eea7b) turned out to be
far too aggressive on real e-ink hardware: every navigation black-flashes,
which is worse than the ghosting it was clearing. Remove the whole mechanism —
DisplayDriver::forceFullRefresh() virtual, GxEPDDisplay's _force_full flag and
override, the endFrame() branch, and the setCurrScreen() call. E-ink is back to
interval-only full refreshes (Settings > Full refresh interval).

The favourites "(gone)"-tile prune that shipped in the same commit is kept.

Builds green: WioTrackerL1Eink_companion_solo_dual.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

examples/companion_radio/ui-new/UITask.cpp

@@ -1923,10 +1923,6 @@ void UITask::setCurrScreen(UIScreen* c) {
   // that mistake is an inert no-op instead of a null deref in render()/poll().
   if (!c) return;
   curr = c;
-  // E-ink: force a full refresh on the first frame of the new screen so leftover
-  // ghosting from the previous screen is cleared (the N-partials interval alone
-  // doesn't catch navigation). No-op on OLED.
-  if (_display) _display->forceFullRefresh();
   c->onShow();          // central per-visit reset hook (see UIScreen::onShow)
   _next_refresh = 100;
 }