Remove prune step from deployment for now

It doesn't affect greenkeeper subdirectories, which are the ones that cause the most issues. And now the prune step itself is breaking builds. So until it works better, remove this step.

.travis.yml

@@ -58,11 +58,6 @@ deploy:
     condition: $TRAVIS_EVENT_TYPE != cron
   skip_cleanup: true
   script: npm run deploy -- -x -e $TRAVIS_BRANCH -r https://${GH_TOKEN}@github.com/${TRAVIS_REPO_SLUG}.git
-- provider: script
-  on:
-    all_branches: true
-    condition: $TRAVIS_EVENT_TYPE != cron
-  script: npm run prune -- https://${GH_TOKEN}@github.com/${TRAVIS_REPO_SLUG}.git
 - provider: script
   on:
     branch: develop