don't count deleted enrollments in grade calculations

fixes CNVS-16876

Test plan:
  * make a course with 3 enrollments
  * delete one of the enrollments
  * grade the other 2 enrollments on an assignment
  * the assignment stats in 'assignment details' in gb2 should be
    correct
  * the assignment stats on the students grade page should match

Change-Id: Id750f2ff767d83318542bdfca5f2994867b95c8a
Reviewed-on: https://gerrit.instructure.com/45098
Reviewed-by: Mike Nomitch <mnomitch@instructure.com>
Reviewed-by: Josh Simpson <jsimpson@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Amber Taniuchi <amber@instructure.com>
Product-Review: Cameron Matheson <cameron@instructure.com>

app/controllers/enrollments_api_controller.rb

@@ -459,7 +459,7 @@ class EnrollmentsApiController < ApplicationController
     if authorized_action(@context, @current_user, [:read_roster, :view_all_grades, :manage_grades])
       scope = @context.enrollments_visible_to(@current_user, :type => :all, :include_priors => true).where(enrollment_index_conditions)
       unless params[:state].present?
-        scope = scope.where("enrollments.workflow_state NOT IN ('rejected', 'completed', 'deleted', 'inactive')")
+        scope = scope.active_or_pending
       end
       scope
     else

app/presenters/grade_summary_presenter.rb

@@ -183,7 +183,7 @@ class GradeSummaryPresenter
   end
 
   def real_and_active_student_ids
-    @context.all_real_student_enrollments.where("workflow_state not in (?)", ['rejected','inactive']).pluck(:user_id).uniq
+    @context.all_real_student_enrollments.active_or_pending.pluck(:user_id).uniq
   end
 
   def assignment_presenters

spec/presenters/grade_summary_presenter_spec.rb

@@ -65,11 +65,16 @@ describe GradeSummaryPresenter do
         @course.disable_feature!(:differentiated_assignments)
       end
       it 'works' do
-        s1, s2, s3 = n_students_in_course(3)
+        s1, s2, s3, s4 = n_students_in_course(4)
         a = @course.assignments.create! points_possible: 10
         a.grade_student s1, grade:  0
         a.grade_student s2, grade:  5
         a.grade_student s3, grade: 10
+
+        # this student should be ignored
+        a.grade_student s4, grade: 99
+        s4.enrollments.each &:destroy
+
         p = GradeSummaryPresenter.new(@course, @teacher, nil)
         stats = p.assignment_stats
         assignment_stats = stats[a.id]