Three tests designated as flaky on Linux have not failed on the
continuous integration server in a long time. Removing flaky designation
for these tests.
Fixes: https://github.com/nodejs/node/issues/4446
PR-URL: https://github.com/nodejs/node/pull/4519
Reviewed-By: Johan Bergström <bugs@bergstroem.nu>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Brian White <mscdex@mscdex.net>
test-tls-ticket-cluster : PASS,FLAKY
[$system==linux]
-test-http-client-timeout-event : PASS,FLAKY
-test-child-process-buffering : PASS,FLAKY
-test-child-process-exit-code : PASS,FLAKY
[$system==macos]