Merge branch 'js/no-more-legacy-stash'

Removal of unused code and doc. * js/no-more-legacy-stash: stash: stop warning about the obsolete `stash.useBuiltin` config setting stash: remove documentation for `stash.useBuiltin` add: remove support for `git-legacy-stash` git-sh-setup: remove remnant bits referring to `git-legacy-stash`