Quiet the "checking uprobes" pass-4 messages

Quiet the "checking uprobes" pass-4 messages

For session.verbose=1, we mostly only print the result of the pass.  We
had a uprobes "preamble" though in pass 4, which IMO was a misleading
break in convention.  It gave the impression that all the building time
for the actual script was part of the uprobes work.

* buildrun.cxx (verify_uprobes_uptodate, make_uprobes): Only print the
  preamble message for verbose > 1.