Rip out version checks

[ekohl]

I realize this is a partial fix that's unlikely to be accepted, but let me make the case and we can see where we can end up. These version checks are highly annoying for multiple reasons.

• They require internet access on every command. This is a privacy concern because it leaks when you're using vagrant. It's also not guaranteed to be available.
• They print warnings to stdout which breaks commands like vagrant ssh-config
• There is no way to deactivate them. I know I installed a custom version because I needed fixes not available in a released version.

[coveralls]

Coverage remained the same at 87.74% when pulling a9d9c46 on ekohl:remove-version-checks into 4ee2d59 on ggiamarchi:master.

[ggiamarchi]

@ekohl As you expected, this PR won't be accepted but I agree this is a real issue.

A fix is provided by #365