Remove excessive logging from label-reachable.h

[shiralal]

No description provided.

[mjansche]

Thanks for your pull request! This repo is an unofficial mirror of OpenFST, and as such it itsn't the right place to incorporate changes. Changes here would not necessarily be reflected upstream, plus this mirror would diverge from the upstream sources. That said, I will reach out to the right people who can perhaps try to see if they would like to incorporate this change upstream.

I will leave this PR open for now, for better visibility.

[agutkin]

Running with verbosity level of 3 already provides excessive amount of diagnostics, so my question would be why run with in such a verbose mode anyway? If running in VLOG(3) mode is necessary (diagnostics is absolutely required), then I suppose one option would be to use VLOG(4) or VLOG(5) here, what do you think?