This reverts commit 64d5899.

Reason for revert: If stdin is large, then the param object can become
an extremely long string, exceeding the maximum OS size limit on
commandline parameters.

Original change's description:
> refactor(exec): remove paramsFile (#807)
>
> The `paramsFile` is obsolete now that we use `execFileSync()` for our
> internal implementation. Instead, we pass parameters to the child
> process directly as a single commandline parameter to reduce file I/O.
>
> Issue #782

Fixes #818