Minor cleanup

[BigRoy]

Changelog Description

• Fix ChannelFilename and ChannelExtension being defined twice
• Improve type hint

Additional review information

I'm a bit confused by SceneOS.

1. The comment states: Possible values are windows, linux, osx
2. get_rr_platform returns windows, linux, mac
3. This page of Royal Render for .xml says: Possible values are windows, linux, osx?
4. This page of Royal Render for .localtex says: Values can be win, lx or mac.

So which is it?

This made me think 2) was wrong on our end, so I changed that to use osx but I'm still confused by 4). But I guess .localtex files just have different SceneOS format.

Testing notes:

1. Check code changes

[kalisp]

1. The comment states: Possible values are windows, linux, osx

This will be more question for @h-schoenberger

[h-schoenberger]

I'm a bit confused by SceneOS.
1. The comment states: Possible values are windows, linux, osx
2. get_rr_platform returns windows, linux, mac
3. This page of Royal Render for .xml says: Possible values are windows, linux, osx?
4. This page of Royal Render for .localtex says: Values can be win, lx or mac.

First: Yes, Localtex is a different file type.
Although the SceneOS specs are the same as for submission xml files:

You may use any of the above values.
windows, linux, osx, win, lx or mac.

Note:
If you do not set SceneOS at all, it uses the OS of the machine that you used to submit
Exception: The output and scene file paths are clearly not matching the OS. (Like \fileserver on Linux.)

[BigRoy]

@kalisp can you check and approve if ok please, ready to merge.