travis.yml: Remove allowed failures.

They don't fail anymore, and they cause notifications to #limnoria
to be duplicated.

.travis.yml

@@ -26,9 +26,6 @@ notifications:
     email: false
 matrix:
   fast_finish: true
-  allow_failures:
-    - python: "nightly"
-    - python: "pypy3" # https://bitbucket.org/pypy/pypy/issues/2129/local-variable-val-referenced-before
   exclude:
     - python: "2.6"
       env: WITH_OPT_DEPS=false