Fixes#1712

This rewords and adds some missing information to the docstring ofSubmodule.remove, for themethod parameter, discussed in#1712. It uses the second suggestion presented in that issue, formatted in the style of the surrounding docstring (an 88-column wrap).

It also does some other rewording in that docstring, for clarity, at the end of that same section (on themethod parameter), and a small punctuation fix in the section about theforce parameter.

A note on coordination

Please note that, while this is not a behavioral change, I believe an ordinary patch release rather than a "post" release should be made if this is included. In particular, although I discussed doing a "post" release in#1715, a release that includes both this change and the changes from#1715 should be a normal 3.1.39 release. (In contrast, if this modified only files such asREADME.md or documentation indoc/, then a post release would make sense.)