rsync: automate Windows binary maintenance

rsync: automate Windows binary maintenance

Sources from msys2 rather than cygwin because msys2 uses ~standard
pacman which allows a linux build server to fetch the current bins
cleanly, also msys2 has newer rsync and openssl.

Increases minimum Windows rsync OS requirement to Windows 10 x64,
see https://www.msys2.org/docs/windows_support/

Removes redundant copy and chmod batch steps.
The chmod was a workaround only needed due to running rsync with
--executability (needed on linux but it was probably a mistake to use it
on windows where it causes problems due to windows' lack of a direct
equivalent of the unix execute permission).

Reduces remaining batch spam.