Remove UseLlvmOpt option
Remove UseLlvmOpt option

According to my records, the option is not used. It was added when
we started using the curated list of passes.

Removing the option will simplify transition to the new pass manager.

GPUOpen-Drivers/llpc,GPUOpen-Drivers/llpc,GPUOpen-Drivers/llpc,GPUOpen-Drivers/llpc,GPUOpen-Drivers/llpc