Remove out of date references and fields on User registration page

Problem/Motivation

The current user/registration page has out of date information and fields which relate to past events. This is confusing for new contributors.

Proposed resolution

Update the registration form!

Remaining tasks

1. Remove out of date fields.

Delete these fields:

Will attend/attended activities at DrupalCon Denver
Wed BoF: Work with a core maintainer or initiative owner to write a lesson (Wed 3:45pm - 4:45pm in room 502)
Thurs BoF: Brainstorm and prioritize features for learndrupal.org and Learn Drupal distribution (Thurs 10:45am - 11:45am in room 502)
Fri Sprint: Participate in Learn Drupal distro development (details will be emailed)

2. Update text to reflect new naming of the project DrupalLadder.

3. Review current "I'm interested in" fields to relate to the correct sub-components of the DrupalLadder project:

Bringing the Boston Initiative to my hometown
Organizing an Issue Sprint (2-hour meetup activity)
Organizing a Learn Sprint (1-hour meetup activity)
Writing a lesson
Helping build or maintain learndrupal.org
Theming learndrupal.org / Learn Drupal distro
Module development / install profile development for the Learn distro
Helping with project management