Update examples for probing with systemtap

Update examples for probing with systemtap

This removes the old example for legacy probes and adds two
new scripts demonstrating many of the new probe point facilities.

The rpc-monitor.stp script will print out friendly details of all
RPC traffic between a libvirt client/server. This is incredibly
useful in seeing what RPC calls are being made, and also debugging
problems in the RPC protocol code

The events.stp script will print out lots of info about the poll
event loop, which is useful for debugging event handling problems

* examples/systemtap/events.stp, examples/systemtap/rpc-monitor.stp:
  New examples
* examples/systemtap/client.stp: Remove obsolete example