message: build_system: remove unused variable
diff: @@ -5,9 +5,6 @@ include_directories(
  SYSTEM ${CMAKE_SOURCE_DIR}/third_party/mavlink/include
  )
  -# These are consumed in ../CMakeLists.txt
  -set(integration_tests_src ${integration_tests_src} PARENT_SCOPE)
  -
  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -DTESTING")
  # `make test` does not show output, but `make check` does
  