Remove external network E2E from flake finder

These tests sporadically fail and the original dev is no longer involved
with the project so there's no one to maintain them.

Parallel to #2827.

Signed-off-by: Daniel Farrell <dfarrell@redhat.com>

.github/workflows/flake_finder.yml

@@ -23,7 +23,6 @@ jobs:
             extra-toggles: ovn
         include:
           - extra-toggles: globalnet, ovn
-          - extra-toggles: external-net
     steps:
       - name: Check out the repository
         uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11