Fix: duplicated definition of llndk_headers module

A llndk_headers module was double defined; one as a header lib and the
other as a static lib. Since llndk_headers is a header lib, the static
lib is now deleted.

Bug: 70617292
Test: build. (TestLlndkHeaders added)
Change-Id: I1a3e9d1a73616ea4faf03664a7a4b03bd5955629