libmachine: API version is the rpc protocol version, its not used here

The protocol version is used in the rpc server and client. We don't
directy use it here.

Author: guillaumerose

pkg/libmachine/version/version.go

@@ -1,9 +1,6 @@
 package version
 
 var (
-	// APIVersion dictates which version of the libmachine API this is.
-	APIVersion = 1
-
 	// ConfigVersion dictates which version of the config.json format is
 	// used. It needs to be bumped if there is a breaking change, and
 	// therefore migration, introduced to the config file format.