This commit removes attempts to auto-detect the version of the local
Tmux binary.
The Tmux package that ships with OpenBSD doesn't have a version
number[1], and therefore doesn't provide any way to check if it's
compatible with the REPL module, making the feature disabled by
default in that distribution.
Fixes#3237.
[1] https://github.com/tmux/tmux/issues/1141#issuecomment-340244302
7b9ae595c0