Remove the qpid-cpp C++ client from the repo, and simplify (remove boost)

[jiridanek]

We can remove qpid-cpp because upstream is not releasing new versions and therefore Red Hat is unlikely to ship it. If this changes, use a branch of this repo that will still have the client.

Removing the code here will allow to delete some duplication, simplify the cmake build.

1. create branch containing old code
2. remove -DENABLE_MODERN, that is, reapply what had to be removed in Revert "Set -DENABLE_MODERN flag to ON by default and remove it (#66)" #69
3. remove remaining boost dependency, that is probably the significant part done in work by intern, Port fixes made by intern #17

[jiridanek]

1. qpid-cpp branch is https://github.com/rh-messaging/cli-cpp/tree/qpid-cpp