must statements in leaf-refs towards capability data

[PrathibaJee]

For the Proposal in the issue openBackhaul/core#27 , need to remove the substatement "must 'deref(.) = current()'" from the leafref statement.

Solution :
In the UML2YANG tool in the experimental branch , require to remove the following code from the files tools/xmi-to-yang/src/main/resources/model ,

• yang/leaf.js: type += "\t\t\t\tmust 'deref(.) = current()';\r\n";
• yang/leaf-list.js: type += "\t\t\t\tmust 'deref(.) = current()';\r\n";