CMake: Removed unused variable (thanks, Felix!). "MACOSX_COREAUDIO" is actually an internal #define set up elsewhere, and this CMake var is never exported past the CMake script anyhow. Partially fixes Bugzilla #2807.
diff --git a/CMakeLists.txt b/CMakeLists.txt
index fff35a5..6baff8a 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1051,7 +1051,6 @@ elseif(APPLE)
if(SDL_AUDIO)
set(SDL_AUDIO_DRIVER_COREAUDIO 1)
- set(MACOSX_COREAUDIO 1)
file(GLOB AUDIO_SOURCES ${SDL2_SOURCE_DIR}/src/audio/coreaudio/*.c)
set(SOURCE_FILES ${SOURCE_FILES} ${AUDIO_SOURCES})
set(HAVE_SDL_AUDIO TRUE)