Revert "test: add test cases for fsPromises"

This reverts commit c05c73a6.

The commit breaks Raspberry Pi CI.

PR-URL: https://github.com/nodejs/node/pull/19101
Ref: https://github.com/nodejs/node/pull/19064#issuecomment-370092633


Reviewed-By: Daijiro Wachi <daijiro.wachi@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>