Revert "feat: allow synthetic default imports when testing typescript for esm"

[d-goog]

Reverts #203

We actually do not want allowSyntheticDefaultImports here (affecting all Node.js TypeScript repos) as it may hide runtime issues within our system tests:

If they encountered an error with import *, it may have appeared as if enabling allowSyntheticDefaultImports would fix it, but in fact it only silenced the build-time error while emitting code that would crash in Node.

Source: https://www.typescriptlang.org/docs/handbook/modules/appendices/esm-cjs-interop.html

Instead, in places where we are relying on a default, we should use import * as something from 'file.ts' appropriately.

[sofisl]

This PR relies on this setting currently. Can we get tests passing here without the setting before merging this PR?