Removed leave buttons from settings dropdowns

app/views/layouts/nav/_group_settings.html.haml

app/views/layouts/nav/_project.html.haml

app/views/shared/members/_access_request_buttons.html.haml

...23305-leave-project-and-leave-group-should-be-buttons.yml

...ures/groups/members/last_owner_cannot_leave_group_spec.rb

spec/features/groups/members/member_leaves_group_spec.rb

spec/features/groups/members/user_requests_access_spec.rb

...s/members/group_member_cannot_leave_group_project_spec.rb

.../group_requester_cannot_request_access_to_project_spec.rb

spec/features/projects/members/member_leaves_project_spec.rb

...tures/projects/members/owner_cannot_leave_project_spec.rb