Revert "[Cashtab] Add code splitting to improve initial load time"

Summary:
This reverts commit 3f8b1475be898f37609576cf5778eaf2efde8607.

I accidentally based this on D18218

it's breaking CI I think due to a rebase conflict in the package.json; has the package-lock.json from D18218 but not the package.json

Test Plan: npm test

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Differential Revision: https://reviews.bitcoinabc.org/D18225