Remove dependency to log4j

Vaadin itself is using java.util.logging and there were only 2 logging statements in whole lazyquerycontainer so it does not make much sense to create dependency to specific 3rd party logging library.
Plugin consumers using other than JDK logging (e.g. slf4j) usually ship some delegate layer (e.g. jcl-over-slf4j) to switch to their preferred logging framework.