Remove old excludes

These are detected as errors since the clean up was done[1] in
the requirements repository.

[1] 314734e938f107cbd5ebcc7af4d9167c11347406

Change-Id: I1c29b201dcd3702c09b9b8b6ea15a85d22227366

doc/requirements.txt

@@ -1,6 +1,3 @@
-# The order of packages is significant, because pip processes them in the order
-# of appearance. Changing the order has an impact on the overall integration
-# process, which may cause wedges in the gate later.
 openstackdocstheme>=2.2.1 # Apache-2.0
 reno>=3.1.0 # Apache-2.0
-sphinx>=2.0.0,!=2.1.0 # BSD
+sphinx>=2.0.0 # BSD

requirements.txt

@@ -1 +1 @@
-pbr!=2.1.0,>=2.0.0 # Apache-2.0
+pbr>=2.0.0 # Apache-2.0

test-requirements.txt

@@ -1,4 +1,4 @@
-coverage!=4.4,>=4.0 # Apache-2.0
+coverage>=4.0 # Apache-2.0
 stestr>=2.0.0 # Apache-2.0
 # sphinx is needed for testing the sphinxext module
-sphinx>=2.0.0,!=2.1.0 # BSD
+sphinx>=2.0.0 # BSD