Remove msys-bash in favor of the upstream version

Bash 3.1.23-1 is upstream, incl. Kirill's patch to not load user32.dll for
every shell process, so we can rid of maintaining it.

Signed-off-by: Sebastian Schuberth <sschuberth@gmail.com>
Merge pull request #29 from sschuberth/master

Remove msys-bash in favor of the upstream version