[llvm] [offload] Add early exit on plugin deinit when offloading is disabled (PR #134090)

[Joseph Huber via llvm-commits]

https://github.com/jhuber6 commented:

Does this really make a difference? The previous patch made sure that none of the plugins are initialized, which means that this is just a loop over a handful of pointers, which is well within the noise for performance testing.

https://github.com/llvm/llvm-project/pull/134090