[llvm] [Dexter] Make lldb-dap _post_step_hook more stable (PR #157663)

[Stephen Tozer via llvm-commits]

https://github.com/SLTozer approved this pull request.

LGTM to fix the buildbots and remove the temp code, though a clearer idea of why we don't have the modules available (and more importantly whether Dexter can fix that) would be good in the longer term.

https://github.com/llvm/llvm-project/pull/157663