makefile: DRY out pkg targets (#9643)
makefile: DRY out pkg targets (#9643)

This removes small differences between the targets, like the statement
about what's being built.

The CGO/Windows related comments were deleted as being not relevant. 
See https://github.com/hashicorp/nomad/pull/9643 for context.
dvusboy/nomad,dvusboy/nomad,dvusboy/nomad,hashicorp/nomad,burdandrei/nomad,hashicorp/nomad,dvusboy/nomad,dvusboy/nomad,hashicorp/nomad,dvusboy/nomad,burdandrei/nomad,hashicorp/nomad,hashicorp/nomad,burdandrei/nomad,burdandrei/nomad,burdandrei/nomad,burdandrei/nomad,burdandrei/nomad,dvusboy/nomad,hashicorp/nomad