test: Remove unused mock
test: Remove unused mock

This just spews out lots of warnings, and the mock interface is never
used. This makes it harder to analyze with test failures.

Change-Id: I5c71da0806012dd5945f2f7ca19eb27b538c9571
Signed-off-by: William A. Kennington III <30fff5198f4d10ca1117e5f3ec82f3b4b8900d81@google.com>

openbmc/phosphor-networkd,openbmc/phosphor-networkd