docs/INSTALL.rst: drop python2 related bits
@@ -65,10 +65,9 @@ interacting with the services to schedule tests and to report the test results.
Update Dependencies
-------------------
-We track the dependencies using ``requirements.txt``
-for python2 and python3 respectively. These packages are tested, and should work
-with teuthology. But if you want to bump up the versions of them, please use the
-following command to update these files::
+We track the dependencies using ``requirements.txt`` . These packages are
+tested, and should work with teuthology. But if you want to bump up the
+versions of them, please use the following command to update these files::
./update-requirements.sh
