Remove the now-EOL 3.3

Author: tianon

.travis.yml

@@ -17,10 +17,6 @@ env:
   - VERSION=3.4 VARIANT=jessie/slim
   - VERSION=3.4 VARIANT=wheezy
   - VERSION=3.4 VARIANT=alpine3.4
-  - VERSION=3.3 VARIANT=jessie
-  - VERSION=3.3 VARIANT=jessie/slim
-  - VERSION=3.3 VARIANT=wheezy
-  - VERSION=3.3 VARIANT=alpine3.4
   - VERSION=2.7 VARIANT=stretch
   - VERSION=2.7 VARIANT=jessie
   - VERSION=2.7 VARIANT=jessie/slim