[Libguestfs] [PATCH nbdkit] locks: Remove debugging messages about

[Richard W.M. Jones]

The messages are not really useful to us, but they do bloat the
debugging output of virt-v2v massively:

nbdkit: python[1]: debug: acquire global request lock
nbdkit: python[1]: debug: acquire per-connection request lock
nbdkit: python[1]: debug: acquire unload prevention lock
nbdkit: python[1]: debug: pwrite count=2097152 offset=4628414464 fua=0
nbdkit: python[1]: debug: release unload prevention lock
nbdkit: python[1]: debug: release per-connection request lock
nbdkit: python[1]: debug: release global request lock

We probably need some kind of level of verbosity to deal with this
sort of thing, but that's quite a large change.

Rich.