Remove 'esm' package dependency

[jribbink]

Instructions

Remove the ESM loader. It should not be used as the package is abandoned and does not support newer ECMAScript features and this is a very non-standard way of running ESM scripts.

Issue To Be Solved

We should not be using the esm loader.

(Optional): Suggest A Solution

Bundle the CLI to CJS as another entry point in addition to the existing bundle created for flow-js-testing. This could involve switching from microbundle to @onflow/fcl-bundle as this offers some utility with multiple entry points and creation of CLI bundles.