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>

src/helpers/ui/DisplayDriver.h

@@ -272,7 +272,6 @@ public:
   virtual void setBrightness(uint8_t level) { }  // level 0-4 (min to max), no-op default
   virtual void setDisplayRotation(uint8_t rot) { }  // 0-3, no-op for fixed-orientation displays
   virtual void setFullRefreshInterval(uint8_t n) { }  // e-ink: do full refresh every n partial refreshes (0=never)
-  virtual void forceFullRefresh() { }  // e-ink: make the next frame a full (non-partial) refresh — clears ghosting on screen change; no-op on OLED
   virtual void endFrame() = 0;
 
 #ifdef ENABLE_SCREENSHOT