don't query asv for needs grading count

unnecessary because submissions are deleted
by duedatecacher now

closes #CORE-1653

Change-Id: I2abd3ab4051263ec8a5964c77be85d3937c10147
Reviewed-on: https://gerrit.instructure.com/158031
Tested-by: Jenkins
Reviewed-by: Spencer Olson <solson@instructure.com>
Reviewed-by: Jeremy Stanley <jeremy@instructure.com>
Product-Review: James Williams  <jamesw@instructure.com>
QA-Review: James Williams  <jamesw@instructure.com>

app/models/assignments/needs_grading_count_query.rb

@@ -139,10 +139,6 @@ module Assignments
           AND e.workflow_state = 'active'
           AND #{Submission.needs_grading_conditions}
         SQL
-
-      string += <<-SQL
-        AND EXISTS (SELECT * FROM #{AssignmentStudentVisibility.quoted_table_name} asv WHERE asv.user_id = submissions.user_id AND asv.assignment_id = submissions.assignment_id)
-      SQL
       joined_submissions.where(string, assignment, course)
     end