Project: clear `decltype` and `declvalue` when project is no longer declarative

Dependencies

• [2] JTEQTE7Y Project: delete the `.jobsets` jobset if project is no longer declarative
• [*] FPK5LF53 * Put the project-related actions in a separate controller. Put the
• [*] 6WRGCITD Enable declarative projects.

Change contents

• edit in src/lib/Hydra/Controller/Project.pm at line 174
  [2.80]

  [5.703]
  + $project->update(

  + { decltype => ""

  + , declvalue => ""

  + });