services/mgmt/lib/testutil: Remove some dead code and unexport unused functions.
services/mgmt/lib/testutil: Remove some dead code and unexport unused
functions.

Change-Id: Ie8ad346e2c0f22f94d571cc18fcf6426ab8ba11b

vanadium/go.ref,vanadium/go.ref,vanadium/go.ref,vanadium/go.ref,vanadium/go.ref,vanadium/go.ref