Build/Test tools: Remove the unnecessary clone of the twentysixteen repo.

This is no longer needed since #31550.

Fixes #40066

Merges [40252] to the 4.7 branch.


git-svn-id: https://develop.svn.wordpress.org/branches/4.7@40253 602fd350-edb4-49c9-b593-d223f7449a82

.travis.yml

@@ -36,7 +36,6 @@ matrix:
   - php: hhvm
   - php: nightly
 before_install:
-- git clone https://github.com/WordPress/twentysixteen.git src/wp-content/themes/twentysixteen
 - |
   if [[ "$WP_TRAVISCI" == "travis:phpunit" ]]; then
       mysql -u root -e "CREATE DATABASE wordpress_tests;"