WPCOM: Migrate wpcom.undocumented() site plans to wpcom.req

[tyxla]

Changes proposed in this Pull Request

This PR migrates all the wpcom.undocumented() site plans method to wpcom.req.get().

The PR also simplifies the code a little bit - we don't need to encode the site fragment, because anywhere in the code where we're making requests to this endpoint, we pass the numeric site ID. There is no longer a reason to support non-numeric IDs there - we removed that support a while ago. We're also removing an unnecessary wrapping Promise - wpcom.req.get() already returns a promise.

We also use the opportunity to remove the unused cancelSitePlanTrial action creator, its related reducer and tests and the unused undocumented cancelPlanTrial method. It was created almost 6 years ago in #2952 and it hasn't been used yet, so it's time to go.

Part of the ongoing effort to get rid of wpcom.undocumented().

Testing instructions

• Go to /plans/:site where :site is one of your Jetpack sites.
• Verify that the request to /sites/:site/plans is still successful.
• Verify the removed code is not in use.

[github-actions]

Link to Calypso live: https://calypso.live?image=registry.a8c.com/calypso/app:build-18761
Link to Jetpack Cloud live: https://calypso.live?image=registry.a8c.com/calypso/app:build-18761&env=jetpack

[matticbot]

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

App Entrypoints (~163 bytes removed 📉 [gzipped])

name                   parsed_size           gzip_size
entry-main                  -697 B  (-0.1%)     -163 B  (-0.0%)
entry-login                 -486 B  (-0.1%)     -137 B  (-0.1%)
entry-gutenboarding         -349 B  (-0.0%)     -103 B  (-0.0%)
entry-domains-landing       -349 B  (-0.1%)     -103 B  (-0.1%)

Common code that is always downloaded and parsed every time the app is loaded, no matter which route is used.

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.

[jsnajdr]

Looks good 👍 Nice find that cancelSitePlanTrial was unused.