No, you can't delete the braces (they aren't really characters in the internal representation of the file; they're just for display).
What you can do is this:
- Display the field code. Turn on nonprinting characters (click the ¶ button on the Home tab).
- Click to the left of the first real character inside the field code.
- Use the vertical scroll bar and/or the scroll wheel (if your mouse has one) to bring the end of the document into view -- DO NOT use the arrow keys or the Page Up/Down keys, which move the cursor.
- Hold the Shift key while you click to the right of the last real character in the field code. That selects all of the code but not the braces.
- Cut the selected text to the clipboard.
- Delete the field (which is now just two braces with a couple of spaces inside them).
- Paste from the clipboard.