[RBAC] remove 'project_member' credentias

There is no need to use 'project_member 'credentials
in reader class.

Change-Id: I80e7e1ccef4ef3ef45e2a013610602e003deaf84
diff --git a/manila_tempest_tests/tests/rbac/test_share_types.py b/manila_tempest_tests/tests/rbac/test_share_types.py
index 2263747..e4e6016 100644
--- a/manila_tempest_tests/tests/rbac/test_share_types.py
+++ b/manila_tempest_tests/tests/rbac/test_share_types.py
@@ -155,7 +155,7 @@
 
 class ProjectReaderTests(ShareRbacShareTypesTests, base.BaseSharesTest):
 
-    credentials = ['project_reader', 'project_member']
+    credentials = ['project_reader']
 
     @decorators.idempotent_id('f4c352c4-c12b-4722-9fe7-9a2ec639ee63')
     @tc.attr(base.TAG_NEGATIVE, base.TAG_API)