Do not warn if sun.reflect.Reflection.getCallerClass() is unavailable

Modern Java releases disallow the access to internal sun.* API. There
is not much the user can do about it, hence this warning is not
actionable and therefore unneeded.

It also does not tag its origin, causing confusion among users about
its whereabouts.

Author: Flowdalic

log4j-api/src/main/java/org/apache/logging/log4j/util/StackLocator.java

@@ -77,7 +77,6 @@ public final class StackLocator {
                 }
             }
         } catch (final Exception | LinkageError e) {
-            System.out.println("WARNING: sun.reflect.Reflection.getCallerClass is not supported. This will impact performance.");
             getCallerClassMethod = null;
             java7u25CompensationOffset = -1;
         }