requirements: Drop references to os-testr

We now use stestr, which was only being included because it's a
requirement of os-testr.

Change-Id: I4c7cd309fb23b60f6a7458547647e081d7755a1c
Signed-off-by: Stephen Finucane <stephenfin@redhat.com>

lower-constraints.txt

@@ -52,7 +52,6 @@ openstacksdk==0.12.0
 os-api-ref==1.5.0
 os-client-config==1.29.0
 os-service-types==1.2.0
-os-testr==1.0.0
 osc-lib==1.10.0
 oslo.cache==1.29.0
 oslo.concurrency==3.26.0

test-requirements.txt

@@ -7,7 +7,7 @@ coverage>=4.5.1 # Apache-2.0
 fixtures>=3.0.0 # Apache-2.0/BSD
 nose>=1.3.7 # LGPL
 oslotest>=3.3.0 # Apache-2.0
-os-testr>=1.0.0 # Apache-2.0
+stestr>=2.0.0 # Apache-2.0
 pylint==1.4.5 # GPLv2
 python-subunit>=1.2.0 # Apache-2.0/BSD
 testrepository>=0.0.20 # Apache-2.0/BSD