Preparing for removal of RSTUDIO_MSYS_SSH

[kevinushey]

The version of ssh.exe bundled with RStudio on Windows is now quite old, and we're considering removing it in a future release. We'd then like to rely on the versions of ssh.exe bundled with Windows, or otherwise direct users to download an SSH client themselves (or even use the one provided as part of Git for Windows).

I see parallely tries to make use of this SSH client if available:

https://github.com/HenrikBengtsson/parallelly/blob/199705bfa3957112c4c85bcff6a62f93fcff241f/R/utils%2Ccluster.R#L115-L132

Is this going to cause trouble for parallely, or are you able to rely on other available SSH installations?