To hide field labels on a Donation page, simply find the field in question, go to its associated tab in the administrator's view of the Donation page, and then click on the "Customize Headings and Labels" button. From there, find the field you wish to change its description, then under that field's description text box, choose "Hide" and save the page.
For example, if you wanted to hide the description that appears under the dedication section's email field...
1) Navigate to the Donation form you wish to affect
2) Go: Payment tab > Dedication section > Customize Headings and Labels button > Notification Email Address Description field: and then choose the "Hide" option
2) Click Save button