test: remove flaky designation from fixed tests

`test-tls-ticket-cluster` and `test-vm-syntax-error-stderr` are no
longer flaky.

Refs: https://github.com/nodejs/node/issues/2510
Refs: https://github.com/nodejs/node/issues/2660
PR-URL: https://github.com/nodejs/node/pull/5459


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>