7
It's a link to the developer's site inviting for a donation to help support his ongoing work. Lots of modules do this or, at least, have a link to the developer's site. It is not compulsory to donate.
Many modules have a link to the developer's site openly visible to all viewers but you say that this link is only visible in the admin side. If so then, why are you bothered by it? Is it too much to ask to leave it there bearing in mind that the developer has made the module available for free but could have incurred costs in doing so.... server space rental, etc?
Please check the licence to see if you are permitted to remove it before doing so and respect the module author's wishes in this regard. Who knows, in times to come you may develop a module of your own and be in the same position
