Fix spotless (#136334)

Fixes a spotless error for #136311

Author: jdconrad

x-pack/plugin/core/src/test/java/org/elasticsearch/xpack/core/security/authc/AuthenticationTests.java

@@ -51,7 +51,6 @@
 import static org.hamcrest.Matchers.hasKey;
 import static org.hamcrest.Matchers.is;
 import static org.hamcrest.Matchers.not;
-import static org.hamcrest.Matchers.notNullValue;
 import static org.hamcrest.Matchers.nullValue;
 import static org.hamcrest.Matchers.sameInstance;