Fix geometry optimiser

[VReaperV]

Fixes #1651

I opted for making the hash not use uv's instead, as it didn't seem to have much of any effect on the loading time, but resulted in merging a few more vertices.

Also fixed sky brushes being added as surfaces to the material system.

[slipher]

The commit Don't hash the uv's in geometry optimiser does the opposite of its description. It adds them back to the hash, while the previous commit removes them.

[VReaperV]

The commit Don't hash the uv's in geometry optimiser does the opposite of its description. It adds them back to the hash, while the previous commit removes them.

Fixed.

[slipher]

The station15 sun disappears when material system is enabled.

(There should be a sun)

[slipher]

illwieckz has said the station15 sun uses something called a "skybox portal". (You can see 2 copies of it if noclipping.) I have no idea where this implemented in the code. There is a flag called RF_SKYBOXPORTAL but it's never set anywhere, so apparently unrelated.

[VReaperV]

The station15 sun disappears when material system is enabled.

(There should be a sun)

Fixed.

[slipher]

LGTM