Remove helptags test from travis

This is tested in test/help.vim

Author: thinca

.travis.yml

@@ -37,7 +37,6 @@ script:
   - uname -a
   - which -a vim
   - vim --cmd version --cmd quit
-  - vim --cmd "try | helptags doc/ | catch | cquit | endtry" --cmd quit
   # - /tmp/vim-themis/bin/themis --runtimepath /tmp/vimproc --reporter dot
   - /tmp/vim-themis/bin/themis --runtimepath /tmp/vimproc --exclude ConcurrentProcess --reporter dot
   - ruby scripts/check-changelog.rb