Delete superfluous frame_config.duration comment
diff --git a/lang/builtin/builtin.go b/lang/builtin/builtin.go
index b2fddb1..efce8f3 100644
--- a/lang/builtin/builtin.go
+++ b/lang/builtin/builtin.go
@@ -351,7 +351,6 @@
 	"token_writer.available() u64",
 
 	// ---- frame_config
-	// Duration's upper bound is the maximum possible i64 value.
 
 	"frame_config.blend() u8",
 	"frame_config.disposal() u8",