CMake: unit-tests: Make lorawan stub only depend on headers it uses

Previously the connectivity lorawan stub library depended on
`mbed-headers`, which is a collection of all available headers
in mbed-os. To make it easier to separate the library, only depend
on the headers we're using.

Author: rajkan01

connectivity/lorawan/tests/UNITTESTS/doubles/CMakeLists.txt

@@ -41,8 +41,12 @@ target_sources(mbed-stubs-lorawan
 
 target_link_libraries(mbed-stubs-lorawan
     PRIVATE
-        mbed-headers
-        mbed-headers-lorawan
+        mbed-headers-base
+        mbed-headers-events
+        mbed-headers-hal
         mbed-stubs-headers
+        mbed-headers-connectivity
+        mbed-headers-platform
+        mbed-headers-lorawan
         gtest
 )