test: remove flaky designation for test
Unreliability for test-trace-events-fs-sync is believed to have been fixed. Remove flaky designation.
Ref: https://github.com/nodejs/node/pull/22812 Ref: https://github.com/nodejs/node/issues/21038#issuecomment-421199960
Checklist
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make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
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