Remove maxlength from signup description textfield

First, thanks for the recent changes and the 2.1 version. Everything is working spectacularly.

While setting up our newsletter using the "Single checkbox" approach, I wanted to include a rather verbose description below the checkbox including a link to our privacy policy and newsletter information page. This all told read like this:

We will never share your e-mail with anyone. See our <a href="http://example.com/privacy">Privacy policy</a> and information about our <a href="http://example.com/newsletter">newsletter</a>.

Unfortunately the description field is capped at 128 characters (the Drupal default unless something else is specified). My description ran about 200 characters once the HTML for the links is included, but I could see some people having descriptions of full paragraphs. I propose that we just take off the maxlength property entirely by setting it to NULL.