[ORC][examples] Remove ThinLtoJIT example after LLJITWithThinLTOSummaries landed in OrcV2Examples

The ThinLtoJIT example was aiming to utilize ThinLTO summaries and concurrency in ORC for speculative compilation. The latter is heavily dependent on asynchronous task scheduling which is probably done better out-of-tree with a mature library like Boost-ASIO. The pure utilization of ThinLTO summaries in ORC is demonstrated in OrcV2Examples/LLJITWithThinLTOSummaries.