server: replace blob prefix separator from ':' to '-' (#3146)

This fixes issues with blob file names that contain ':' characters to be rejected by file systems that do not support them.

server/images.go

@@ -795,9 +795,7 @@ func PruneLayers() error {
 
 	for _, blob := range blobs {
 		name := blob.Name()
-		if runtime.GOOS == "windows" {
-			name = strings.ReplaceAll(name, "-", ":")
-		}
+		name = strings.ReplaceAll(name, "-", ":")
 		if strings.HasPrefix(name, "sha256:") {
 			deleteMap[name] = struct{}{}
 		}