Bug 2220: Incorrect override of getUnknownNodes in TypeDefinitionBuilderImpl

In TypeDefinitionBuilderImpl there is override of getUnknownNodes method
which returns Collections.emptyList().
The override method has been removed from TypeDefinitionBuilderImpl.

Change-Id: I7a7121965848b7feceeac2e6e832b2f93049b576
Signed-off-by: pkajsa <pkajsa@cisco.com>