test: remove flaky designation for test_threadsafe_function
The test_threadsafe_function doesn't seem to be flaky anymore on Windows. Optimistically removing the flaky designation in the relevant status file.
Refs: https://github.com/nodejs/node/issues/23621#issuecomment-468938980
Will close https://github.com/nodejs/node/issues/23621 before landing this.
Checklist
-
make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
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