Remove legacy keycodes, part 4 (#18683)

* `KC_PGDOWN` -> `KC_PGDN`

* `KC_PSCREEN` -> `KC_PSCR`

* `KC_SCOLON` -> `KC_SCLN`

* `KC_BSLASH` -> `KC_BSLS`

* `KC_BSPACE` -> `KC_BSPC`

users/arkag/arkag.c

@@ -458,7 +458,7 @@ bool process_record_user(uint16_t keycode, keyrecord_t *record) {
       }
       return false;
 
-    case KC_BSPACE:
+    case KC_BACKSPACE:
       if (record->event.pressed) {
         state = active;
         velocikey_accelerate();