tech debt: remove use of AbortController

https://github.com/adobe/aio-cli-plugin-app/blob/fff25048d2a506acd825761f049a103e490821f8/src/BaseCommand.js#L13-L14

AbortController was an emergency hotfix because some dependency updated to use node-14 at the time without bumping a major. AbortController was first in [node 14.17](https://developer.mozilla.org/en-US/docs/Web/API/AbortController#browser_compatibility)

Open src/BaseCommand.js at lines 13-14 and read how AbortController is used in the base command. Confirm the old Node.js compatibility rationale, then remove the AbortController use and verify that no such use remains in the file and the CLI behavior is unchanged.

Written by the indexing model from the issue text.