Removes etcd2 code and images.
Etcd2 is no longer supported as of 1.13, so rollback and management
tools for etcd2 should not be shipped any longer. If it is still desired
the older versions of the image can be used.
Change-Id: I516c40067f0a57c42d2a6ab4612071c5e556a005
This file is not used anywhere.
Further more, this is an error in this file:
```
$ flake8 third_party/htpasswd/htpasswd.py --select=F
third_party/htpasswd/htpasswd.py:46:13: F821 undefined name 'time'
```
Ts is go/types forked from go@236abdb46b (just after 1.10) and
cherry-picked go@1006f703ffc, which fixes https://github.com/golang/go/issues/23712.
It can be removed when all builders are >= go1.11.
