chore(build): Remove redundant tsconfig settings

[lobsterkatie]

This removes two tsconfig settings which don't have any effect given settings elsewhere in the repo:

• noEmitHelpers: The TS config docs aren't super clear in saying this explicitly, but noEmitHelpers has no effect in the presence of importHelpers: true, because the latter means that no helper implementations will be emitted in any case, instead being imported from tslib.

• Node types: We've had Node types in our repo-level tsconfig for a long time, but all packages which need Node types already specify it themselves. Removing it in our top-level tsconfig also has the advantage that it means we won't accidentally use Node types where we shouldn't (like in browser-based and cross-platform packages).