Add "Remove From Lists" option under the All Available Bookmarks window in the My Bookshelf bar.
Currently, the only way to remove an item from a list is by clicking into the list itself and selecting the materials. Since the All Available Bookmarks feature is the first in the Bookmarks tab, it makes sense that there would also be an option to remove materials there.

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Laurie Shedrick commented
Agreed- having the option to manage should be in all views.
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Kathryn Brew commented
When looking at All Available in the new bookshelf feature, the only option for selected items is to Place Holds.
But when you are within a list, you can select items and also Add to Lists or Remove from List. People are used to those options, and it would be especially useful to have a Remove button to quickly un-bookmark titles while looking at the All Available view.
For people who don’t create multiple lists, and just use For Later, it's unintuitive to exit out of All Available and scroll down to the list in order to remove bookmarks. We have a staff member whose workflow was to select multiple titles, place holds, then remove the bookmarks. In the new view, the remove option wasn't where they expected it to be.