Do not set microversion for server diagnostics negative test

After microversion 2.48, response data from each hypervisor
differs from that before 2.48, so microversion is set in
test_server_diagnostics.py, but for server diagnostics negative
test("Non-admin user cannot view server diagnostic"), there
is no difference between before and after 2.48, so no need to
set microversion for server diagnostics negative test.

Change-Id: I0c256aa58258de934fd6e49cc5e1ef6b8ab1abd6
diff --git a/tempest/api/compute/admin/test_server_diagnostics_negative.py b/tempest/api/compute/admin/test_server_diagnostics_negative.py
index d5b6674..6215c37 100644
--- a/tempest/api/compute/admin/test_server_diagnostics_negative.py
+++ b/tempest/api/compute/admin/test_server_diagnostics_negative.py
@@ -18,8 +18,6 @@
 
 
 class ServerDiagnosticsNegativeTest(base.BaseV2ComputeAdminTest):
-    min_microversion = None
-    max_microversion = '2.47'
 
     @classmethod
     def setup_clients(cls):
@@ -33,8 +31,3 @@
         server_id = self.create_test_server(wait_until='ACTIVE')['id']
         self.assertRaises(lib_exc.Forbidden,
                           self.client.show_server_diagnostics, server_id)
-
-
-class ServerDiagnosticsNegativeV248Test(ServerDiagnosticsNegativeTest):
-    min_microversion = '2.48'
-    max_microversion = 'latest'