The links in /etc/rc?.d/ point to scripts in /etc/init.d/. As for brltty, it sounds like an accesibility feature for some Braille thing.

First, try to find out to which package it belongs:

$ dpkg -S /etc/init.d/brltty 

brltty: /etc/init.d/brltty

Well, that's clear, the brltty package is responsible for this. Let's get more information about it:

Excerpt from apt-cache show brltty:

Description-en: Access software for a blind person using a braille display

 BRLTTY is a daemon which provides access to the console (text mode)

 for a blind person using a braille display.  It drives the braille

 display and provides complete screen review functionality.

You can safely remove it, nothing really depends on it if you do not have a braille display (checked with apt-cache rdepends brltty)