fix(types): remove reference to @types/webxr

[Methuselah96]

When type-checking an app with @react-three/fiber installed (and skipLibCheck set to false) there is an error resolving @types/webxr despite those types never being used:

ERROR in ./node_modules/@react-three/fiber/dist/declarations/src/core/store.d.ts:1:23
TS2688: Cannot find type definition file for 'webxr'.
  > 1 | /// <reference types="webxr" />
      |                       ^^^^^
    2 | import * as THREE from 'three';
    3 | import * as React from 'react';
    4 | import { GetState, SetState, StoreApi, UseBoundStore } from 'zustand';

This PR fixes the error by specifying the types property which prevents @types/webxr from being included in the compilation unnecessarily.

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