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

keyboards/gboards/gergoplex/matrix.c

@@ -152,11 +152,6 @@ uint8_t matrix_scan(void) {
     return 1;
 }
 
-bool matrix_is_modified(void)  // deprecated and evidently not called.
-{
-    return true;
-}
-
 inline bool         matrix_is_on(uint8_t row, uint8_t col) { return (matrix[row] & ((matrix_row_t)1 << col)); }
 inline matrix_row_t matrix_get_row(uint8_t row) { return matrix[row]; }