try with only one extra

setup.py

@@ -268,6 +268,7 @@ setup(name="tahoe-lafs", # also set in __init__.py
               "pytest-twisted",
               "hypothesis >= 3.6.1",
               "treq",
+              "towncrier",
           ],
           "tor": [
               "foolscap[tor] >= 0.12.5",
@@ -277,9 +278,6 @@ setup(name="tahoe-lafs", # also set in __init__.py
               "foolscap[i2p] >= 0.12.6",
               "txi2p >= 0.3.2", # in case pip's resolver doesn't work
           ],
-          "release": [
-              "towncrier",
-          ],
       },
       package_data={"allmydata.web": ["*.xhtml",
                                       "static/*.js", "static/*.png", "static/*.css",

tox.ini

@@ -26,7 +26,7 @@ deps =
 # We add usedevelop=True for speed, and extras=test to get things like "mock"
 # that are required for our unit tests.
 usedevelop = True
-extras = test,release
+extras = test
 commands =
          tahoe --version
          trial {env:TAHOE_LAFS_TRIAL_ARGS:--rterrors} {posargs:allmydata}