small header adjustment

I couldn't build plug-ins. It was complaining that `QSTargetPickerPanel.h` was missing. All the other header files in the interface framework were marked as "Public". Setting this one to match seems to fix it, so that's what I did.

This also removes some references to the new plug-in update interface that snuck in with the help enhancements. I didn't do anything to remove them. Looks like Xcode just figured it out when I fiddled with the header above.

This is on my master branch, since I assume it'll go in quickly. If no one says anything tomorrow, I'll just merge it myself. :-)