GWF-translator doesn't identify elements by system identifier

[MksmOrlov]

Describe the bug
gwf translator doesn't identify elements by the same system identifier

To Reproduce
Steps to reproduce the behavior:

1. Create gwf like that, place it in kb directory
   
2. run ./build_kb
3. see translated scs like that:

@link_123 = _[ ];;
@link_123 => nrel_system_identifier: _link_1;;
class_1 -> @link_123;;

@link_456 = _[ ];;
@link_456 => nrel_system_identifier: _link_1;;
class_2 -> @link_456;;

And @link_123 and @link_456 are different sc-elements.

Expected behavior
@link_123 and @link_456 are the same. I can find _link_1 and both classes: class_1 and class_2