Finally! I've finished cleaning out my shelves now. Why I ever added some of these books is beyond me, but now they're gone or on a more appropriate shelf. Here's how it all ended up:
"to-read-1001-books" - 548
I didn't remove or add any to this list. In fact, I'm not done adding books to it yet.
"to-read-adult" - 209
"to-read-classic" - 33
No adds or removals here either.
"to-read-fantasy" - 176
"to-read-historical" - 49
"to-read-new-adult" - 128
"to-read-non-fiction" - 81
Added this shelf while doing this; these books were shifted to here from previously existing shelves.
"to-read-science-fiction" - 82
"to-read-young-adult" - 330
I added two new shelves as well: reviews-says-no for those books friends/trusted reviewers had reviewed and that let me know the book is not for me. The other was waiting for reviews for a few books I'm hesitant to read and will wait for friends to read and I'll see what they thought of it.
I also have won't bother and we are never getting together. The first is for books I've lost interest in, and the second is for books I wouldn't touch even with a stick (either due to its content or to badly behaving authors). Let's just say these two shelves expanded a great deal.
All in all, I think I removed around 500 books. At least I can't say it wasn't productive. Perhaps I have a slight chance of finishing my lists some day. Or they will grow whenever I see a pretty cover. We'll see.