HistoryGuru#updateRepositories() is dead code

[vladak]

The code for updating (mirroring) repository contents in HistoryGuru (and update() methods in various repositories) has never been used AFAIK - it is only called from HistoryGuruTest. This duplicates the work currently done by mirror.py.

It should be decided how mirroring will be done and either enhance the update code (it lacks e.g. support for proxies, proper logging or hooks) and make it available via RESTful API or rip it out and live with mirror.py.

[vladak]

Given that in the mean time a fairly elaborate set of scripts was introduced that facilitates the work done by update, let's remove it.