tevent: Remove python module.

tevent: Remove python module.

This module didn't have any functionality that we actually used yet, and
it was quite small.

Tevent is quite low level and perhaps doesn't make much sense to expose
directly as a Python module. It was also causing build problems when used with a
system-tevent. We can always back later if necessary.
(cherry picked from commit 5065cf70f8bf41193d6d33413f2285f62bba0502)
(cherry picked from commit 1d0e302bc49c77542fa39a18d995268e8685d141)