[vrouter-netns] Fix requirements

Remove requirements pointed to modules delivered in the standard python
library.

Change-Id: Ifa3549502bbbdd5cf91795a5932e1900db31f9c3
(cherry picked from commit f21dea9ce62c355cb37393ae3adf4d348d37b34c)
Merge "[vrouter-netns] Fix requirements" into R1.10