Use loadCubeMapTexture instead of CubeTextureLoader for light probes

[mrxz]

Fixes #5734

Description:
Probe lights used an instance of THREE.CubeTextureLoader to create a CubeTexture which was then fed into the LightProbeGenerator. With #5454 the possible values for srcs for an envMap were broadened, meaning they were no longer guaranteed to be URLs, but could also contain HTMLImageElement.

The loadCubeMapTexture method on the material system already handles all possible values. This PR replaces the light component to use loadCubeMapTexture instead of manually using a CubeTextureLoader instance.

Changes proposed:

• Use loadCubeMapTexture when loading a cubemap texture for light probes

[dmarcos]

Thank you!