Rip out client directory fetch instrumentation

In the distant past, weasel put in a feature where clients would track number of bytes they receive by what category of directory information, and then you could query the current sums via the dirport ("GET /tor/bytes.txt"). It went into 0.2.1.1-alpha I think (see git commits 01c1a355 and 716558a), but it didn't get a changelog entry or a trac ticket, and also it only works #if defined(INSTRUMENT_DOWNLOADS) || defined(RUNNING_DOXYGEN).

I don't think anybody is using it now, and nobody in the Montreal Meeting wanted to keep it, so it looks like we should simplify by removing it.

I am cc'ing weasel since it was his feature originally, and now he can speak up in favor of its life if he wants.