In P7  whenever i added a runtime I would also delete a runtime so i would not have too many files loaded.  I have about 46 external runtimes. iirc in P7 there was a "-" sign next to the "+".  But i cannot see a way to do that in PP2010. Sorry if this has been answered elsewhere or if i am missing the obvious.

Use the pulldown:

Show Library: Some Individual Library

instead of  

This makes the library GUI focused on just one library.

Then the remove button will appear.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)

Thank you very much for the quick reply bagginsbill!