fmt: remove misleading comment fragment

src/libcore/fmt/mod.rs

@@ -1275,7 +1275,7 @@ pub fn write_fmt(&mut self, fmt: Arguments) -> Result {
         write(self.buf, fmt)
     }
 
-    /// Flags for formatting (packed version of rt::Flag)
+    /// Flags for formatting
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn flags(&self) -> u32 { self.flags }