Issue tracking the removal of the PWA category

• deprecation warning banner
• remove the category from the json result
• remove/rearrange PWA audits
• ensure support for report PWA category rendering post removal
• remove references to documentation in codebase
• Get rid of ServiceWorker gatherer
• Get rid of Manifest/InstallabilityErrors gatherers and ManifestValues computed artifact
• unlist Lighthouse PWA documentation in the report
• clean up PWA Github issues

a nice have, but not a blocker for releasing this - would need some more investigation on this one.

• maybe include a no_pointless_service_worker audit