tests/avocado: Use default CPU for pseries machine

Use the default CPU with the pseries machine unless there is a
specific requirement.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
diff --git a/tests/avocado/migration.py b/tests/avocado/migration.py
index 09b62f8..be6234b 100644
--- a/tests/avocado/migration.py
+++ b/tests/avocado/migration.py
@@ -123,7 +123,6 @@
     """
     :avocado: tags=arch:ppc64
     :avocado: tags=machine:pseries
-    :avocado: tags=cpu:power9_v2.0
     """
 
     def test_migration_with_tcp_localhost(self):