CSS3DRenderer: Remove perspective component from style when scene is being rendered with an orthographic camera

[soadzoor]

So, here's the deal in a longer story:
I implemented a new feature into one of my projects: ability to change the cameratype realtime (Orthographic vs Perspective).
So I noticed the following: By default, it's Orthographic. If I change it to Perspective, then back to Orthographic, the CSS3D parts look weird. I investigated this problem a bit, and found that the "perspective" component of the style attribute is added when the camera is a perspectivecamera, but it doesn't get removed when the camera is an orthographic camera.

This PR fixes the issue.

[Mugen87]

@yomotsu Does this change look good to you?

[yomotsu]

Thanks for letting me know @Mugen87 🙇‍♂️

I took a look at the PR.
It makes sense. Here is the reason we need to remove the style for orthographic camera
#13790 (comment)

Here is the current r109 with the problem.
(Camera type can be changed with the button)
https://jsfiddle.net/0uta1xro/1/

And here is the fixed one with the PR
https://jsfiddle.net/0uta1xro/

LGTM👍

[yomotsu]

wait! This PR is changing JSM.

@soadzoor please change /js file. /jsm is generated from /js.

[mrdoob]

I'll fix the js file post-merge.

[mrdoob]

Thanks!

[mrdoob]

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