moved Lutz to alumni section

[Rock-n-Rolli]

• moved Lutz
• removed link to Kerstin's chair webpage as it could not be rendered correctly
  @hamzaibrahim21 if it is easy we could also think about adding the possibility to add links to co-supervisors, as this is currently only possible for active members.

[hamzaibrahim21]

@Rock-n-Rolli I added the hyperlink for the co-supervision as it was done before.

@AndreaVolkamer I implemented it the old way, though I can update it to use hyperlinks as we did with the team members. Let me know which approach you'd prefer.
Also I was thinking of removing any unnecessary data from the alumni, e.g. Github, linkedin, anything that will not be visible in the alumni section, what do you think ?