Remove the stats gatherer and supporting code

[exarkun]

Since at least 1.13.0 it has not been possible to run the stats gatherer.

One person did notice this (​https://tahoe-lafs.org/trac/tahoe-lafs/ticket/2940) but it sounds like a new user, not someone actually using the stats gatherer or related functionality in the real world. Since there have been no other reports of its breakage, a reasonable conclusion seems to be that no one actually uses this functionality.

Operational visibility into the Tahoe-LAFS software is a very important thing for any real deployments and gathering metrics from the software itself is likely an essential part of obtaining this visibility. However, a custom stats aggregator custom-built for Tahoe-LAFS is probably not a requirement for this. Instead, there are a number of widely deployed third-party systems for collecting such metrics. Many of them also hook into more powerful visualization systems than Munin (which is what all of the Tahoe-LAFS stats stuff is geared towards).

I propose that we re-build Tahoe-LAFS' operational visibility features with one of these more powerful systems.

As a first step in that direction, we should remove all of the existing "stats gatherer" and related support code. This will clear the way for new work. If this were a regression then it would be a bad plan but the regression already happened years ago.

[exarkun]

​https://github.com/tahoe-lafs/tahoe-lafs/pull/920

[GitHub <noreply@…>]

In d096cc5/trunk:

Merge pull request #920 from tahoe-lafs/3549.remove-stats-gatherer

Remove the stats gatherer

Fixes: ticket:3549