[llvm] [EXEGESIS][NFC] Remove unused 'ExecJIT' (PR #98119)

[Aiden Grossman via llvm-commits]

https://github.com/boomanaiden154 commented:

I don't think we can get rid of this. `ExecJIT` owns the memory that the JITed code is emitted into. By letting it get destroyed when it falls out of scope during creation of `ExecutableFunction`, the memory it owns (including the assembled snippet) gets released, leading to potential errors when we try to invoke the snippet later on.

Trying out the patch locally, I'm seeing tests fail, presumably due to this issue.

https://github.com/llvm/llvm-project/pull/98119