Remove ebtables_driver/manager dead code

Remove ebtables_driver/manager dead code

Previous changes[1] have been merged as enablers[2] to fix the bug
1274034 but an alternative solution has been choosen and now we can
consider the introduced code as dead code.

This changes removes [2], associated tests and rootwrap filters.

[1] I9ef57a86b1a1c1fa4ba1a034c920f23cb40072c0
    I3c66e92cbe8883dcad843ad243388def3a96dbe5
[2] neutron.agent.linux.ebtables_driver
    neutron.agent.linux.ebtables_manager

Closes-Bug: #1493422
Related-Bug: #1274034
Change-Id: I61e38fc0d8cf8e79252aabc19a70240be57e4a32