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

[Shilei Tian via llvm-commits]

shiltian wrote:

> There was a problem in downstream code containing an OMPT trace-record-manager which is assumed to be valid. So this early exit prevents that problem. It seems symmetric enough for both init() and deinit() to have this early exit. And less divergence between upstream and downstream. 
> 
> 
> 
> What do you think, @jhuber6 

My $.02 is to fix it in downstream, since the code doesn't exist upstream. This extra check doesn't make any difference with upstream code.

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