Remove obsolete build-status indicator

It currently shows as red, but it has actually been replaced by a new workflow.
We could replace with the new workflow, but it seems wiser to not include this in the README to begin with to avoid future regressions. People can always check the health of the projects in the Actions tab.

Signed-off-by: Steffen Smolka <smolkaj@google.com>

Author: smolkaj

README.md

@@ -69,7 +69,7 @@ may need to change the permissions manually for the generated files after the
 These commands are the ones used by our CI system to ensure that the Protobuf
 files stay semantically valid.
 
-## Build Using Bazel ![build protobufs](https://github.com/p4lang/p4runtime/workflows/build%20protobufs/badge.svg)
+## Build Using Bazel
 
 The protobufs can also be built using [Bazel](https://bazel.build/).
 The Bazel WORKSPACE and BUILD files are located in the [proto folder](proto/).