Fix expire_status warning (#15094)

Marlin/src/lcd/ultralcd.h

           static millis_t progress_bar_ms;  // Start time for the current progress bar cycle
           static void draw_progress_bar(const uint8_t percent);
           #if PROGRESS_MSG_EXPIRE > 0
-            static millis_t MarlinUI::expire_status_ms; // = 0
+            static millis_t expire_status_ms; // = 0
             static inline void reset_progress_bar_timeout() { expire_status_ms = 0; }
           #endif
         #endif