remove 'covr' from Suggests, remove unused importFrom

[jameslamb]

Some cleanup of dependencies.

• removes {covr} from Suggests:
  • {covr} is only used in CI scripts here, not for anything CRAN sees
  • removing it from Suggests makes reverse dependency checking a little cheaper for CRAN and for {covr} maintainers... and avoids the need to install {covr} to check {uptasticsearch}
• removes import of stringr::str_detect()
  • [ci] add more {lintr} linters #234 removed the only use of it
• re-renders the docs with {roxygen2} 7.3.2 (the latest version)