Revert "[lldb] [test] Add synchronization to TestContinue"

This reverts commit 7aadecae.

I'm reverting this commit because it appears to break the green dragon
incremental LLDB bot.

https://reviews.llvm.org/D131758

See LLDB Incremental buildbot: https://green.lab.llvm.org/green/view/LLDB/job/lldb-cmake/46215/execution/node/70/log/