[MtoA] Renderman performance warning

If you have both Renderman and MtoA installed, you may see a warning that says “Arnold for Maya degrades Renderman performance.” Unless you are running a version of MtoA from 20 months ago, this performance warning is false. MtoA does not degrade Renderman performance.

This was fixed in Arnold (fix #4393 main thread was pinned to a single core) back in January 2015.