[tahoe-lafs-trac-stream] [Tahoe-LAFS] #2766: remove unnecessary dependencies

[Tahoe-LAFS]

#2766: remove unnecessary dependencies
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 Reporter:  warner     |          Owner:  daira
     Type:  task       |         Status:  new
 Priority:  normal     |      Milestone:  eventually
Component:  packaging  |        Version:  1.11.0
 Keywords:             |  Launchpad Bug:
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 Let's remove `characteristic` right now, it's a throwback to some old
 pyopenssl thing, and the only place it exists at all in our depenency
 graph is in tahoe's `_auto_deps.py`.

 Let's remove the transitive dependencies: things we claim to depend upon
 but never import:

 * pyopenssl
 * service-identity
 * pyasn1-modules
 * pyasn1

 Let's do a global `s/simplejson/json/` and stop depending on the
 `simplejson` module. The `json` in stdlib should be enough. (This is a
 leftover from the days of python2.5(?) that didn't have stdlib `json`, but
 now we require py2.7).

 We need to retain `twisted[tls]` instead of just `twisted` because pip
 lacks a resolver.

 Not a part of this ticket:

 * #2098 : get zfec to remove dependency on pyutil/zbase32

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Ticket URL: <https://tahoe-lafs.org/trac/tahoe-lafs/ticket/2766>
Tahoe-LAFS <https://Tahoe-LAFS.org>
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