obs-webrtc: Fix CMake 3.0 module disabled path

The CMake 3.0 path used the old syntax for logging if the module was
disabled. Update this to use target_disable to match the syntax in other
CMake 3.0 paths.

plugins/obs-webrtc/CMakeLists.txt

@@ -4,7 +4,7 @@ legacy_check()
 
 option(ENABLE_WEBRTC "Enable WebRTC Output support" ON)
 if(NOT ENABLE_WEBRTC)
-  message(STATUS "OBS:  DISABLED   obs-webrtc")
+  target_disable(obs-webrtc)
   return()
 endif()