Remove mox3 dependencies

Dependency for mox3 is fully removed. So this patch removes mox3
dependency from followings:

- lower-constraints.txt
- test-requirements.txt
- doc/requirements.txt

This should be cherry-picked into stable/rocky branch.

Change-Id: Idd1f095b5f7ae6a4b07153dd7d3587dc18822df6

.stestr/format

@@ -0,0 +1 @@
+1

.stestr/next-stream

@@ -0,0 +1 @@
+0

doc/requirements.txt

@@ -8,7 +8,6 @@
 #
 # Requirements for docs
 mock>=2.0.0 # BSD
-mox3>=0.20.0 # Apache-2.0
 openstackdocstheme>=1.18.1 # Apache-2.0
 reno>=2.5.0 # Apache-2.0
 sphinx!=1.6.6,!=1.6.7,>=1.6.2 # BSD

lower-constraints.txt

@@ -43,7 +43,6 @@ MarkupSafe==1.0
 mccabe==0.2.1
 mock==2.0.0
 monotonic==1.4
-mox3==0.20.0
 msgpack==0.5.6
 munch==2.2.0
 netaddr==0.7.19

test-requirements.txt

@@ -6,4 +6,3 @@ hacking!=0.13.0,<0.14,>=0.12.0 # Apache-2.0
 
 coverage!=4.4,>=4.0 # Apache-2.0
 mock>=2.0.0 # BSD
-mox3>=0.20.0 # Apache-2.0