obs-browser: Only disable NetworkService on macOS

Apparently, using the old chromium network implementation changes the
way cookies are handled, causing cookies to reset.  So instead of doing
that, continue to use the new network implementation on Windows, and
only use the old network implementation on macOS for the time being.

obs-browser @ 1a5f2419

-Subproject commit 8e1279e2994a3b9ecbf87457548e2ddcd27d9eb8
+Subproject commit 1a5f2419e20b5de9aa1abb5a8ab2795444fe41a6