Revert "(Temporarily) readd bare support for py27"

This reverts commit 33a2a5f2e4. We're now
at M1 and the DevStack default has been changed. We no longer need to
pretend to support Python 2.7. This is slightly modified to drop an
additional Python 2.7-only dependency from lower-constraints.txt.

[1] I52b03caee0ba700da3a15035201ea6cd91baa06b

Change-Id: I1068850072e639ee268d68ca82249f569a40310e
Signed-off-by: Stephen Finucane <sfinucan@redhat.com>

lower-constraints.txt

@@ -12,7 +12,6 @@ cffi==1.11.5
 cliff==2.11.0
 cmd2==0.8.1
 colorama==0.3.9
-contextlib2==0.5.5;python_version=='2.7'
 coverage==4.0
 cryptography==2.7
 cursive==0.2.1

requirements.txt

@@ -23,7 +23,6 @@ netaddr>=0.7.18 # BSD
 netifaces>=0.10.4 # MIT
 paramiko>=2.0.0 # LGPLv2.1+
 Babel!=2.4.0,>=2.3.4 # BSD
-enum34>=1.0.4;python_version=='2.7' or python_version=='2.6' or python_version=='3.3' # BSD
 iso8601>=0.1.11 # MIT
 jsonschema>=2.6.0 # MIT
 python-cinderclient!=4.0.0,>=3.3.0 # Apache-2.0

setup.cfg

@@ -6,6 +6,7 @@ description-file =
 author = OpenStack
 author-email = openstack-discuss@lists.openstack.org
 home-page = https://docs.openstack.org/nova/latest/
+python-requires = >=3.6
 classifier =
     Environment :: OpenStack
     Intended Audience :: Information Technology

test-requirements.txt

@@ -3,7 +3,6 @@
 # process, which may cause wedges in the gate later.
 
 hacking>=1.1.0,<1.2.0 # Apache-2.0
-contextlib2>=0.5.5;python_version<'3.0'  # PSF License
 coverage!=4.4,>=4.0 # Apache-2.0
 ddt>=1.0.1 # MIT
 fixtures>=3.0.0 # Apache-2.0/BSD