fix testing issues and clean-up permissions changes

api/base/permissions.py

@@ -170,6 +170,6 @@ def has_object_permission(self, request, view, obj):
         resource = obj['self']
 
         if request.method in permissions.SAFE_METHODS:
-            return resource.is_public or resource.has_permission(auth.user, 'read') or resource.can_view(auth)
+            return resource.is_public or resource.can_view(auth)
         else:
             return resource.can_edit(auth)

api_tests/preprints/views/test_preprint_institutions_relationship.py

@@ -1,6 +1,8 @@
 import pytest
 from api.base.settings.defaults import API_BASE
 from osf_tests.factories import PreprintFactory, AuthUserFactory, InstitutionFactory
+from osf.utils.permissions import READ, WRITE, ADMIN
+
 
 @pytest.mark.django_db
 class TestPreprintInstitutionsRelationship:
@@ -13,21 +15,21 @@ def user(self):
     @pytest.fixture()
     def admin_with_institutional_affiliation(self, institution, preprint):
         user = AuthUserFactory()
-        preprint.add_permission(user, 'admin')
+        preprint.add_permission(user, ADMIN)
         user.add_or_update_affiliated_institution(institution)
         return user
 
     @pytest.fixture()
     def write_user_with_institutional_affiliation(self, institution, preprint):
         user = AuthUserFactory()
-        preprint.add_permission(user, 'write')
+        preprint.add_contributor(user, permissions=WRITE)
         user.add_or_update_affiliated_institution(institution)
         return user
 
     @pytest.fixture()
     def read_user_with_institutional_affiliation(self, institution, preprint):
         user = AuthUserFactory()
-        preprint.add_permission(user, 'read')
+        preprint.add_contributor(user, permissions=READ)
         user.add_or_update_affiliated_institution(institution)
         return user
 
@@ -41,7 +43,7 @@ def no_auth_with_institutional_affiliation(self, institution):
     @pytest.fixture()
     def admin_without_institutional_affiliation(self, preprint):
         user = AuthUserFactory()
-        preprint.add_permission(user, 'admin')
+        preprint.add_contributor(user, permissions=ADMIN)
         return user
 
     @pytest.fixture()