package/macosx: Fix plugins installation

In VLC4 nightly, there are missing plugins. For example building with:

% ../extras/package/macosx/build.sh -i z -a x86_64

librtp_h264_plugin.dylib isn't installed in VLC.app:

% find . -name librtp_h264_plugin.dylib
./modules/.libs/librtp_h264_plugin.dylib
./macos-install/lib/vlc/plugins/access/rtp/librtp_h264_plugin.dylib

Actually the plugin count differs between macos-install folder and VLC.app:

• macos-install/lib/vlc/plugins => 366
• VLC.app/Contents/Frameworks/plugins => 360

With the patch:

% find . -name librtp_h264_plugin.dylib
./VLC.app/Contents/Frameworks/plugins/librtp_h264_plugin.dylib
./modules/.libs/librtp_h264_plugin.dylib
./macos-install/lib/vlc/plugins/access/rtp/librtp_h264_plugin.dylib

And VLC.app has 366 plugins.