test: fix lint error
Fix lint error introduced 03550a5c1e. Unused module fs
is removed.
Refs: https://github.com/nodejs/node/pull/15832#issuecomment-335808467
Checklist
-
make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
commit message follows commit guidelines
Affected core subsystem(s)
test