This plugin allows for you to reorder spells in the Spellbook.
Right-click the Spellbook button and click Enable spellbook reordering, after that move or hide whichever spells you want.
After you're done making changes, right-click the Spellbook button again and click Disable spellbook reordering to properly hide any selected spells, and to prevent dragging spells around when trying to click them.