Temporarily disable tunnel mode flush CTS-V test

This section of CTS-V is still under development and is not ready for
release, but there have been reports of this test failing. Disabling
until the section is ready.

Bug: 176459599
Test: Start CtsVerifier
Test: Navigate to Tunnel Mode section
Test: Verify there is no "Video Codec flushing" test
Change-Id: I53b734ca4674fba0980cfa817411f56c3fb8c0c0