Remove defunct SonarQube plugin link (fixes #2292)

README.md

@@ -113,10 +113,6 @@ Services and platforms that have ShellCheck pre-installed and ready to use:
 * [CircleCI](https://circleci.com) via the [ShellCheck Orb](https://circleci.com/orbs/registry/orb/circleci/shellcheck)
 * [Github](https://github.com/features/actions) (only Linux)
 
-Services and platforms with third party plugins:
-
-* [SonarQube](https://www.sonarqube.org/) through [sonar-shellcheck-plugin](https://github.com/emerald-squad/sonar-shellcheck-plugin)
-
 Most other services, including [GitLab](https://about.gitlab.com/), let you install
 ShellCheck yourself, either through the system's package manager (see [Installing](#installing)),
 or by downloading and unpacking a [binary release](#installing-a-pre-compiled-binary).