Remove unused charset constant in GenericContainer (#8304)

Author: dreis2211

core/src/main/java/org/testcontainers/containers/GenericContainer.java

@@ -71,7 +71,6 @@
 import java.lang.reflect.InvocationTargetException;
 import java.lang.reflect.Method;
 import java.lang.reflect.UndeclaredThrowableException;
-import java.nio.charset.Charset;
 import java.nio.file.Path;
 import java.nio.file.Paths;
 import java.time.Duration;
@@ -112,8 +111,6 @@ public class GenericContainer<SELF extends GenericContainer<SELF>>
     extends FailureDetectingExternalResource
     implements Container<SELF>, AutoCloseable, WaitStrategyTarget, Startable {
 
-    private static final Charset UTF8 = Charset.forName("UTF-8");
-
     public static final int CONTAINER_RUNNING_TIMEOUT_SEC = 30;
 
     public static final String INTERNAL_HOST_HOSTNAME = "host.testcontainers.internal";