Remove the restriction of trial_end date

- This removes the restriction so we can mark expired trials in
customers as expired in gitlab, and be consistent about providing trial
dates, regardless of if it’s in the past or not.

ee/lib/ee/api/namespaces.rb

@@ -116,10 +116,8 @@ module EE
 
             namespace = find_namespace!(params[:id])
             subscription = namespace.gitlab_subscription
-            trial_ends_on = params[:trial_ends_on]
 
             not_found!('GitlabSubscription') unless subscription
-            bad_request!("Invalid trial expiration date") if trial_ends_on&.past?
 
             subscription_params = declared_params(include_missing: false)
             subscription_params[:trial_starts_on] ||= subscription_params[:start_date] if subscription_params[:trial]

ee/spec/requests/api/namespaces_spec.rb

@@ -410,15 +410,6 @@ RSpec.describe API::Namespaces do
           expect(gitlab_subscription.reload.trial_ends_on).to eq(date)
         end
       end
-
-      context 'when the attr has an old date' do
-        it 'returns 400' do
-          do_put(namespace.id, admin, params.merge(trial_ends_on: 2.days.ago.to_date))
-
-          expect(response).to have_gitlab_http_status(:bad_request)
-          expect(gitlab_subscription.reload.trial_ends_on).to be_nil
-        end
-      end
     end
   end
 end