Remove 'projects' and 'shared_projects' from Groups API responses in API V5.

Based on the requirement from !20023 (merged), we are now limiting the number of projects and shared_projects in Groups API response to 100.

But this number (100) is arbritary and does not provide correction information about projects, in case the number of projects in the group is above 100.

Also, GET /groups/:id/projects API and GET /groups/:id/projects/shared API already serves the purpose of exposing project and shared project details within a group in a paginated fashion.

Hence, the plan is to get rid of projects and shared_projects information from Groups API responses, when we release API v5.