README.md: Remove HiL Badge

Since the HAW-Hamburg hack and change to the RIOT community server
the HiL is not operating.  We should remove it until it is brought
back. likely with some improvements and with different links.

Author: MrKevinWeiss

README.md

@@ -1,5 +1,4 @@
 [![Nightly CI status master][master-ci-badge]][master-ci-link]
-[![Nightly HiL CI overview][hil-ci-badge]][hil-ci-link]
 [![GitHub release][release-badge]][release-link]
 [![License][license-badge]][license-link]
 [![API docs][api-badge]][api-link]
@@ -165,5 +164,3 @@ https://www.riot-os.org
 [twitter-link]: https://twitter.com/RIOT_OS
 [wiki-badge]: https://img.shields.io/badge/docs-Wiki-informational.svg
 [wiki-link]: https://github.com/RIOT-OS/RIOT/wiki
-[hil-ci-link]: https://hil.riot-os.org/results/nightly/latest/overview
-[hil-ci-badge]: https://img.shields.io/badge/CI-HiL-blue