[DiapDealer]

Sorry but no. Sigil might fix some invalid code when you allow it to, but it's not going to remove perfectly valid code as part of its Mend or Prettify features (nor is it going to diddle the content of what another application placed in the clipboard before pasting it).

You can easily create a clip to find/remove the comments you don't want, and even assign a keyboard shortcut to the clip for convenience. A plugin can also be written to do something similiar. This is just not something that's a good candidate for inclusion in Sigil's core functionality, I'm afraid.