Remove Fennec from Socorro tests

Some tests are failing because of missing Fennec pages [1], [2] and KaiRo in #breakpad said we should not be testing any Fennec pages anymore.

[1] http://qa-selenium.mv.mozilla.com:8080/view/Socorro/job/socorro.prod/284/testReport/
[2] http://qa-selenium.mv.mozilla.com:8080/view/Socorro/job/socorro.stage/269/testReport/