These flags were not being used because GNUmakefile overwrites them with
another value. We also don't want to set `-s -w` since they remove
information that is important for production debug.
In other projects this variable is used to override the default `-dev`
prerelease that is set even if `VersionPrerelease` is empty, but in
Nomad this check is never actually done because this conditional in
`version/version.go` is always false:
```go
func GetVersion() *VersionInfo {
// ...
rel := VersionPrerelease
// ...
if GitDescribe == "" && rel == "" && VersionPrerelease != "" {
rel = "dev"
}
// ...
}
```
This seems like some leftover from a previous release process, but I
decided the leave the code as is.
