Checkout: Remove unused TransactionFlow and dependencies

[sirbrillig]

Changes proposed in this Pull Request

Since #48152 was merged, TransactionFlow is no longer used by anything in calypso. This PR removes it. There are still some parts of used code in lib/store-transactions but that will be removed in other PRs as those functions are moved elsewhere.

Testing instructions

Just make sure that the deleted code is no longer used anymore.

[matticbot]

Test live: https://calypso.live/?branch=remove/transaction-flow

[matticbot]

Here is how your PR affects size of JS and CSS bundles shipped to the user's browser:

Sections (~6215 bytes removed 📉 [gzipped])

name            parsed_size           gzip_size
woocommerce         -7051 B  (-0.3%)    -1533 B  (-0.3%)
site-purchases      -7051 B  (-0.6%)    -1591 B  (-0.5%)
purchases           -7051 B  (-0.5%)    -1468 B  (-0.4%)
checkout            -7051 B  (-0.5%)    -1623 B  (-0.5%)

Sections contain code specific for a given set of routes. Is downloaded and parsed only when a particular route is navigated to.

Async-loaded Components (~1655 bytes removed 📉 [gzipped])

name                                             parsed_size           gzip_size
async-load-calypso-blocks-editor-checkout-modal      -7051 B  (-0.6%)    -1655 B  (-0.6%)

React components that are loaded lazily, when a certain part of UI is displayed for the first time.

Legend

What is parsed and gzip size?

Parsed Size: Uncompressed size of the JS and CSS files. This much code needs to be parsed and stored in memory.
Gzip Size: Compressed size of the JS and CSS files. This much data needs to be downloaded over network.

Generated by performance advisor bot at iscalypsofastyet.com.

[nbloomf]

Looks good!