Stop manually installing eventlet for our py3 tests

0.25.0 is now included in upper-constraints.txt

Related-Change: I04be480829eaf67ce328b2e7f7d7e2f70aaed90e
Change-Id: I5b8ecd82d6915d0e1cb216c423bbcc75c50a6f3d

tox.ini

@@ -36,7 +36,6 @@ setenv = VIRTUAL_ENV={envdir}
 commands =
   find . ( -type f -o -type l ) -name "*.py[c|o]" -delete
   find . -type d -name "__pycache__" -delete
-  pip install -U eventlet@git+https://github.com/eventlet/eventlet.git
   nosetests {posargs:\
       test/unit/account \
       test/unit/cli \
@@ -127,10 +126,7 @@ commands = ./.functests {posargs}
 
 [testenv:func-py3]
 basepython = python3
-# Need to pick up (unreleased as of 2019-03) commit:
-# https://github.com/eventlet/eventlet/commit/f0bc79e
 commands =
-  pip install -U eventlet@git+https://github.com/eventlet/eventlet.git
   nosetests {posargs: \
     test/functional/test_symlink.py \
     test/functional/tests.py}