When https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/4765 was
created, comments were wrapped in `.note-text`, while Markdown previews
were wrapped in `.md.md-preview-holder`. Both `.note-text` and `.md`
included the `md-typography` mixin, but for some reason the bulleted
list styling had previously been only under `.note-text`, rather than
`md-typography`. It could've been moved there, but instead was moved to
a new `bulleted-list` mixin that now became included by both
`.md.md-preview-holder` and `.note-text`.

Since https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/5162,
comments have also been wrapped in `.md`, which means we only need to
define these bulleted list styles there!

Similarly, https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/10909
added table styling to `.md`, `.note-text`, and `.wiki` through the
`markdown-table` mixin.
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/25666 removed it
from `.note-text`, since all `.note-text` elements already have `.md`
too, and copied some of the styling from this mixin into the
`md-typography` mixin which was used by both `.md` and `.wiki`. As of an
earlier commit in this MR, `.wiki` is gone, which means we only still
need it under `.md`.