Add `mdast-util-to-string` as a dependency

[wooorm]

...and remove remark, strip-markdown.

Reason for this is that it’s a lot faster to just stringify the item. Also: there weren’t any tests by I checked it on:

*   foo
*   bar
*   baz

...and the result were still OK :smile:

[vhf]

Thanks, I'll merge and test. I was wondering, will you also rename mdast-util-position and mdast-util-to-string to remark- or not?

[wooorm]

Nope, they won’t because they work with the AST (which keeps the moniker “mdast”)