Remove astroid from global-requirements list

We dropped various linters in https://review.openstack.org/#/c/473094/.
This is a follow-up patch on this.

astroid is only used by pylint and both versions are tightly coupled.
If we force astroid===1.3.8, we cannot install newer pylint like 1.7.1.
It looks good to consider astroid as a linter.

Change-Id: Ib2e78f6a22b7d90a3304b13228c16d76982fbbef

blacklist.txt

@@ -1,5 +1,6 @@
 # linters - each project may have a different version with loose convergence
 # over time.
+astroid
 flake8
 flake8_docstrings
 flake8-import-order

global-requirements.txt

@@ -4,7 +4,6 @@ amqp>=2.1.0,!=2.1.4  # BSD
 anyjson>=0.3.3  # BSD
 appdirs>=1.3.0  # MIT License
 apscheduler # MIT License
-astroid<1.4.0  # LGPLv2.1 # breaks pylint 1.4.4
 autobahn>=0.10.1  # MIT License
 automaton>=0.5.0  # Apache-2.0
 beautifulsoup4  # MIT

upper-constraints.txt

@@ -130,7 +130,6 @@ taskflow===2.13.0
 traceback2===1.4.0
 semantic-version===2.6.0
 tablib===0.11.5
-astroid===1.3.8
 virtualbmc===1.1.0
 deprecation===1.0.1
 SQLAlchemy===1.1.11