Delete http/tests/inspector/layer-navigation.html

This test is super flaky.  It's not really providing any test coverage.

http://test-results.appspot.com/dashboards/flakiness_dashboard.html#group=%40ToT%20Blink&tests=http%2Ftests%2Finspector%2Flayer-navigation.html

TBR=caseq@chromium.org

Review URL: https://codereview.chromium.org/23601036

git-svn-id: svn://svn.chromium.org/blink/trunk@157847 bbb929c8-8fbe-4397-9dbb-9b2b20218538