Remove deprecated alias of test decorators (2/2)

The attr decorator was deprecated during Pike cycle[1] and multiple
cycles have passed since then.

[1] 3b46d27c90

Depends-on: https://review.opendev.org/908551
Change-Id: Ib24acdd68d1639cd0353f40db1bc9a32b3cecae8

releasenotes/notes/cleanup-attr-decorator-alias-78ce21eb20d87e01.yaml

@@ -0,0 +1,5 @@
+---
+upgrade:
+  - |
+    The ``attr`` decorator is no longer available in the ``tempest.test``
+    module. Use the ``tempest.lib.decorators`` module instead.

tempest/test.py

@@ -31,7 +31,6 @@ from tempest.lib.common import api_microversion_fixture
 from tempest.lib.common import fixed_network
 from tempest.lib.common import profiler
 from tempest.lib.common import validation_resources as vr
-from tempest.lib import decorators
 from tempest.lib import exceptions as lib_exc
 
 LOG = logging.getLogger(__name__)
@@ -39,11 +38,6 @@ LOG = logging.getLogger(__name__)
 CONF = config.CONF
 
 
-attr = debtcollector.moves.moved_function(
-    decorators.attr, 'attr', __name__,
-    version='Pike', removal_version='?')
-
-
 at_exit_set = set()