Add (-) icon to GitLab SVG icon pack

As part of https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/14538, we changed the "remove" icon to Font Awesome's minus-circle icon: https://fontawesome.com/icons/minus-circle?style=solid

canvas

We don't yet have this icon in our GitLab SVG icon kit. We should add this icon and replace the Font Awesome icon added in https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/14538 with this one.