Remove `up` shortcut
Remove `up` shortcut

`down` has no shortcuts, so `up` shouldn't for consistency. Plus, `up`
is already short enough.

k0kubun/byebug,k0kubun/byebug,webdev1001/byebug,scalp42/byebug,deivid-rodriguez/byebug,deivid-rodriguez/byebug,guilherme/byebug,webdev1001/byebug,deivid-rodriguez/byebug,os97673/byebug,yui-knk/byebug,yui-knk/byebug,icebreaker/byebug,guilherme/byebug,icebreaker/byebug,guilherme/byebug,k0kubun/byebug,yui-knk/byebug,os97673/byebug,scalp42/byebug