remove redundant test envs

they were just there when we were making sure the env variable shell
selection was working properly in all cases, now that we know it is,
they can be removed.

.travis.yml

@@ -3,10 +3,8 @@ os:
   - osx
 
 env:
-  - TEST_SHELLS="zsh bash"
   - TEST_SHELLS=bash
   - TEST_SHELLS=zsh
-  - HI=mom
 
 install:
   - ./test/support/travisci_deps.sh