Update deps.sh (#5665)

Try fixing macos build.
2to3 from 2.7 is not really used and is interfering with the
installation of Python 3.9, on which one of ffmpeg's dependencies
depends.

.ci/macos/deps.sh

@@ -2,5 +2,6 @@
 
 brew update
 brew unlink python@2 || true
+rm '/usr/local/bin/2to3' || true
 brew install qt5 sdl2 p7zip ccache ffmpeg llvm ninja
 pip3 install macpack