Miscellaneous cleanup

[jake-low]

• Remove an unused component (HomePane, a leftover piece of an old version of the homepage) and move a translation string from that namespace that was used on the homepage to the Home namespace. Delete the other translation strings which were only used by HomePane
• Remove the REACT_APP_VERSION_SEMVER env var which was magically populated at build time, and instead retrieve the version number in JS by importing the project's package.json which is the more typical pattern for this in my experience.
• Remove service worker code that was not in use (thankfully - service workers, especially caching SWs, are super footgunny and really frustrating to debug).