treewide: remove "v" prefix from versions

A semantic version does not have a "v" prefix.
https://semver.org/#is-v123-a-semantic-version

Change-Id: I95aa2014ba3330d33428e57e5f354eabfe6d1423
Reviewed-on: https://review.monogon.dev/c/monogon/+/4170
Tested-by: Jenkins CI
Reviewed-by: Tim Windelschmidt <tim@monogon.tech>
diff --git a/version/stampgo/main.go b/version/stampgo/main.go
index 3f8502c..439dca5 100644
--- a/version/stampgo/main.go
+++ b/version/stampgo/main.go
@@ -106,10 +106,6 @@
 
 	productVersion := values["STABLE_MONOGON_"+flagProduct+"_version"]
 	if productVersion != "" {
-		if productVersion[0] != 'v' {
-			log.Fatalf("Invalid %s version %q: does not start with v", flagProduct, productVersion)
-		}
-		productVersion = productVersion[1:]
 		v, err := semver.NewVersion(productVersion)
 		if err != nil {
 			log.Fatalf("Invalid %s version %q: %v", flagProduct, productVersion, err)
diff --git a/version/version.go b/version/version.go
index 2929684..05fe630 100644
--- a/version/version.go
+++ b/version/version.go
@@ -23,7 +23,7 @@
 // Semver converts a spec.Version proto message into a SemVer 2.0.0 compatible
 // string.
 func Semver(v *spec.Version) string {
-	ver := "v" + Release(v.Release)
+	ver := Release(v.Release)
 	var prerelease []string
 	if git := v.GitInformation; git != nil {
 		if n := git.CommitsSinceRelease; n != 0 {