Kill cruft no longer used/needed by comons.

The 0.0.42 upgrade and switch to the standard pants bootsrap script
killed the need for both build-support/virtualenv and
build-support/python/libvirtualenv.sh.

I also noticed build-support/ivy/ci.ivysettings.xml was unused.

Testing Done:
CI went green here:
  https://travis-ci.org/twitter/commons/builds/75838991

Bugs closed: 409

Reviewed at https://rbcommons.com/s/twitter/r/2641/

.travis.yml

@@ -13,13 +13,14 @@ before_cache:
     # operation).
   - find $HOME/.ivy2/twitter-commons -type f -name "ivydata-*.properties" -print -delete
   - rm -fv $HOME/.ivy2/twitter-commons/*.{css,properties,xml,xsl}
+  # The stats cache contains timestamped reports unused by CI but that
+  # thrash the cache.  Skip caching these.
+  - rm -rf $HOME/.cache/pants/stats
 
 cache:
   directories:
     - $HOME/.cache/pants
     - $HOME/.ivy2/twitter-commons
-    - build-support/pants.venv
-    - build-support/virtualenv.dist
 
 language: java
 

build-support/bin/ci.sh

@@ -60,9 +60,7 @@ banner "CI BEGINS"
 if [[ "${skip_bootstrap:-false}" == "false" ]]; then
   banner "Bootstrapping pants"
   (
-    ./build-support/python/clean.sh && \
-    PANTS_VERBOSE=1 PEX_VERBOSE=1 PYTHON_VERBOSE=1 ./pants;
-    ./pants goals
+    ./pants help
   ) || die "Failed to bootstrap pants."
 fi