internal/versions: remove constraint.GoVersion wrapper

Remove the constraint.GoVersion wrapper as x/tools can now assume >=go1.21.

Change-Id: I3bd0669d28cabc26cf63c299b3eb51c6a6adc0d0
Reviewed-on: https://go-review.googlesource.com/c/tools/+/632356
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Commit-Queue: Tim King <taking@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

go/analysis/passes/buildtag/buildtag.go

@@ -15,7 +15,6 @@ import (
 
 	"golang.org/x/tools/go/analysis"
 	"golang.org/x/tools/go/analysis/passes/internal/analysisutil"
-	"golang.org/x/tools/internal/versions"
 )
 
 const Doc = "check //go:build and // +build directives"
@@ -371,11 +370,6 @@ func (check *checker) finish() {
 
 // tags reports issues in go versions in tags within the expression e.
 func (check *checker) tags(pos token.Pos, e constraint.Expr) {
-	// Check that constraint.GoVersion is meaningful (>= go1.21).
-	if versions.ConstraintGoVersion == nil {
-		return
-	}
-
 	// Use Eval to visit each tag.
 	_ = e.Eval(func(tag string) bool {
 		if malformedGoTag(tag) {
@@ -393,26 +387,19 @@ func malformedGoTag(tag string) bool {
 		// Check for close misspellings of the "go1." prefix.
 		for _, pre := range []string{"go.", "g1.", "go"} {
 			suffix := strings.TrimPrefix(tag, pre)
-			if suffix != tag {
-				if valid, ok := validTag("go1." + suffix); ok && valid {
-					return true
-				}
+			if suffix != tag && validGoVersion("go1."+suffix) {
+				return true
 			}
 		}
 		return false
 	}
 
 	// The tag starts with "go1" so it is almost certainly a GoVersion.
 	// Report it if it is not a valid build constraint.
-	valid, ok := validTag(tag)
-	return ok && !valid
+	return !validGoVersion(tag)
 }
 
-// validTag returns (valid, ok) where valid reports when a tag is valid,
-// and ok reports determining if the tag is valid succeeded.
-func validTag(tag string) (valid bool, ok bool) {
-	if versions.ConstraintGoVersion != nil {
-		return versions.ConstraintGoVersion(&constraint.TagExpr{Tag: tag}) != "", true
-	}
-	return false, false
+// validGoVersion reports when a tag is a valid go version.
+func validGoVersion(tag string) bool {
+	return constraint.GoVersion(&constraint.TagExpr{Tag: tag}) != ""
 }