fix build socket api Mac specific file is now in a subdirectory

Signed-off-by: Matthieu Gallien <matthieu.gallien@nextcloud.com>

src/gui/CMakeLists.txt

@@ -151,7 +151,6 @@ endif()
 
 IF( APPLE )
     list(APPEND client_SRCS cocoainitializer_mac.mm)
-    list(APPEND client_SRCS socketapisocket_mac.mm)
     list(APPEND client_SRCS systray.mm)
 
     if(SPARKLE_FOUND AND BUILD_UPDATER)