Remove Radium from Backpack

Removes Radium from the Backpack component, which is used in Javalab. Also:

• fully removed a :disabled styling that was not being used, and
• cleaned up alignment of list items in the backpack dropdown

List item alignment before

List item alignment after

Testing story

Tested manually in both light and dark mode that hovering on list items and the formatting of the disabled import button appeared the same as they did before moving those styles to SCSS.