Fix fog removal from scene

[mrxz]

Description:
When removing the fog component, the fog wouldn't actually be removed but instead rendered "ineffective" by adjusting the near and far values. This however has two issues:

• Fog type exponential doesn't use near and far meaning the fog would still be visible after removal
• Shaders would still perform fog calculations for no reason

Changes proposed:

• Instead of adjusting fog when removing, outright set it to null (Three.js default value)
• Remove updateMaterials() method as it was only used by the fog component and is not needed since WebGLRenderer: Add support for multiple programs per material. mrdoob/three.js#20135
• Update unit tests to match

[dmarcos]

Thank you!