YARN-7325. Remove unused container variable in DockerLinuxContainerRuntime. Contributed by Shane Kumpf

(cherry picked from commit ce76ed675ebbaa314e3efd847ae96410fadd0d76)

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-nodemanager/src/main/java/org/apache/hadoop/yarn/server/nodemanager/containermanager/linux/runtime/DockerLinuxContainerRuntime.java

@@ -326,7 +326,6 @@ public class DockerLinuxContainerRuntime implements LinuxContainerRuntime {
   @Override
   public void signalContainer(ContainerRuntimeContext ctx)
       throws ContainerExecutionException {
-    Container container = ctx.getContainer();
     PrivilegedOperation signalOp = new PrivilegedOperation(
         PrivilegedOperation.OperationType.SIGNAL_CONTAINER);