There is a work-around which requires some text editing:
Select all notes and export them as an ".enex" file. Open the
file in a text editor and remove the following text
The text may occur multiple times, you need to delete
all occurences. Re-import the modified ".enex"-file in Evernote
and you are done.
Please remember that any changes you do in
one of these notes will not be synced back to Simplenote!