Use correct current page on reader screen

Fixes the page counter not updating

src/screens/EpubReaderScreen.h

@@ -14,7 +14,6 @@ class EpubReaderScreen final : public Screen {
   SemaphoreHandle_t sectionMutex = nullptr;
   int currentSpineIndex = 0;
   int nextPageNumber = 0;
-  int currentPage = 0;
   bool updateRequired = false;
 
   static void taskTrampoline(void* param);