Can not remove header or footer from Civimail e-mail once it has been selected even if you then go back and select none....

Once a header/footer is selected in the CiviMail Wizard, you can not remove it by selecting none. It still appears in the message.

To reproduce:

On step 3 (Mailing Content) of the CiviMail Wizard, go to the Header/Footer section and make sure a Mailing Header or Mailing footer block is selected.
Click Next to advance the Wizard to Step 4 (Test)
Click on the "Preview Mailing", the e-mail should correctly display the header and/or footer.

But, suppose user decides that they didn't really want the header and footer displayed in the message, so they click on "<< Previous" and then select none in the dropdown for Mailing Header and Mailing Footer.

Then click Next to advance to Step 4 again.
click "Preview Mailing" and the header and footer is still part of the mail message.

So, there is now simple way to get rid of the header, footer, once it has been selected, short of starting a whole new e-mail message.