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/metropolis/node/core/update/update.go b/metropolis/node/core/update/update.go
index f241e05..6e41768 100644
--- a/metropolis/node/core/update/update.go
+++ b/metropolis/node/core/update/update.go
@@ -284,7 +284,7 @@
 		RetryNotify: func(err error, d time.Duration) {
 			s.Logger.Warningf("Error while fetching OS image, retrying in %v: %v", d, err)
 		},
-		UserAgent:  "MonogonOS/" + strings.TrimPrefix(version.Semver(mversion.Version), "v"),
+		UserAgent:  "MonogonOS/" + version.Semver(mversion.Version),
 		Scheme:     imageRef.Scheme,
 		Host:       imageRef.Host,
 		Repository: imageRef.Repository,