[Core] Remove matrix_is_modified() and debounce_is_active() (#15349)

keyboards/handwired/promethium/matrix.c

@@ -148,14 +148,6 @@ uint8_t matrix_scan(void)
     return 1;
 }
 
-bool matrix_is_modified(void)
-{
-#if (DEBOUNCE > 0)
-    if (debouncing) return false;
-#endif
-    return true;
-}
-
 inline
 bool matrix_is_on(uint8_t row, uint8_t col)