Revert "Travis: test IPv6-only v3 single onion services on tor master"

This reverts commit 7782b26767c95988255c5d5884df94580e22c5c3.

.travis.yml

@@ -41,9 +41,7 @@ matrix:
       os: osx
       language: c
       python:
-    ## We expect this test to fail, until #23588 is merged into tor master, and
-    ## built into a nightly binary
-    - env: NETWORK_FLAVOUR="single-onion-v23-ipv6-md"
+    - env: NETWORK_FLAVOUR="single-onion-ipv6-md"
       os: osx
       language: c
       python: