[ic] Remove one item from a cart? Limit quantities?

[Kevin Martin]

Hey there.  I'm using 4.9.5 on Linux and have, I think, beaten
the "simple store" from the RTFM tutorial into submission.
(Yay me.)  It's at b3x5c.com (no www) for now, and will move
to a "real" server next month sometime.  Utter newbies are
welcome to ask questions while the problems are still fresh
in my mind. (The "contact us" link goes to my partner, so
please don't use that to take me up on this offer.)

I could use some help on two issues:
 
1) I can't figure out how the snippet in the FAQ allows me to
remove one item from a cart; there's just no context for it.
Can anyone provide that?  I can delete the WHOLE cart, but
that doesn't make for a pleasant shopping experience when
you've picked multiple items and your mouse slips.

2) On a possibly related note, is there a good way to tell
the cart in the "simple store" that it should NOT increment
quantities when an item is picked twice?  We're selling one-
offs, so once a sku is selected there just aren't any more
of it.  I have hardcoded the display so the quantity always
shows as "1" but would like the internals to support it
correctly.

Again, this is the tutorial "simple store," not the Foundation
demo.  I've tried to pick a few enhancements out of that, and
that's how I got the canceled.html page to work, but the rest
of it is WAY too hairy for me. :-)  Thanks!