Remove "experimental" descripton of ACES 2 implementation

[doug-walker]

ACES 2 support was finalized in OCIO 2.4.2 but it is still described a "experimental" in various places in the code.

• OpenColorTypes.h: Update FixedFunctionStyle enum.
• OCIOYaml.cpp: Logs a warning when writing a FixedFunction using one of the ACES 2 styles.
• Config_tests.cpp: Remove the log guard to mute these warnings in various tests.

[killjoycircuit]

Hello, I would like to work on this issue.

[killjoycircuit]

I’ve created a PR for #2196 that updated OpenColorTypes.h file