We are vendoring in several .scss stylesheets that are unused in the codebase. In order to gradually reduce our dependency on Foundation, we should start by removing dead code.

Part of #2972.

Identified stylesheets

• Off Canvas: _offcanvas.scss
• Icon Bar: _icon-bar.scss
• Side Nav: _side-nav.scss
• Magellan: _magellan.scss
• Orbit: _orbit.scss
• Flex Video: _flex-video.scss
• Range Slider: _range-slider.scss
• Pricing Tables: _pricing-tables.scss
• Progress Bars: _progress-bars.scss

Identified removable (but might want to keep)

• Split Buttons: _split-buttons.scss
• Dropdown Buttons: _dropdown-buttons.scss