This gave UID and GID information that wasn't obviously useful to the file
system, given that (by default at least) the file system can only be used by
the mounting user.

It allocates for each call, which is a drag.

The call to commonOp.Logf in sendBazilfuseResponse is extremely hot for
allocations, presumably because it needs to allocate an argument slice.
It is normally not needed at all, so why pay for it?

This saves an allocation that is very much on the hot path in a
read-heavy load.

For GoogleCloudPlatform/gcsfuse#89.