‘EntityOperator#getId()’ is not used in the framework

While reading some code with gil portenseigne we found that ‘EntityOperator#getId()’ is not used anywhere in the framework. it was added in 2010 by doogie in revision 948448 to “Allow for dynamic registering of additional operators for extensions.”.

If this code is still useful outside of the framework, OFBiz should provide a test demonstrated its purpose and describing how to use it. Otherwise we should simply delete it.