I'm also interrested to get rid of prefix and suffix in the webform mail.
I use version webform 6.x-3.18 and I don't find "theme_webform_mail_textfield" anymore as explained in #5 for the support request "Remove Label After Textfield" (webform 6.x-2.29)
I only find function theme_webform_display_textfield($element)
But I want to keep prefix and suffix in the display.
Could you help me?