Update .gitreview for stable/wallaby

This patch also removes the linters from lower-constraints and updates
decorator to 4.4.1 to be consistent with stable/wallaby openstacksdk.

Change-Id: I747a6a9d78519474a6bb340e96c724c20774c450

.gitreview

@@ -2,3 +2,4 @@
 host=review.opendev.org
 port=29418
 project=openstack/python-designateclient.git
+defaultbranch=stable/wallaby

lower-constraints.txt

@@ -7,7 +7,7 @@ cmd2==0.8.0
 coverage==4.0
 cryptography==3.1
 debtcollector==1.2.0
-decorator==3.4.0
+decorator==4.4.1
 deprecation==1.0
 dogpile.cache==0.6.2
 dulwich==0.15.0
@@ -23,7 +23,6 @@ jsonpointer==1.13
 jsonschema==2.6.0
 keystoneauth1==3.4.0
 linecache2==1.0.0
-mccabe==0.2.1
 monotonic==0.6
 mox3==0.20.0
 msgpack-python==0.4.0
@@ -45,11 +44,9 @@ oslo.utils==3.33.0
 oslotest==3.2.0
 paramiko==2.0.0
 pbr==2.0.0
-pep8==1.5.7
 prettytable==0.7.2
 pyasn1==0.1.8
 pycparser==2.18
-pyflakes==0.8.1
 pyinotify==0.9.6
 pyparsing==2.1.0
 pyperclip==1.5.27