Remove helptags test from travis

This is tested in test/help.vim

Author: thinca

.travis.yml

@@ -39,7 +39,6 @@ script:
   - uname -a
   - which -a vim
   - vim --cmd version --cmd quit
-  - vim --cmd "try | helptags doc/ | catch | cquit | endtry" --cmd quit
   - if [ x"$HEAD" = "xyes" ] && [ "$TRAVIS_OS_NAME" != "osx" ]; then sh /tmp/vim-vimlint/bin/vimlint.sh -l /tmp/vim-vimlint -p /tmp/vim-vimlparser -e EVL103=1 -e EVL102.l:_=1 -c func_abort=1 autoload; fi
   # - /tmp/vim-themis/bin/themis --runtimepath /tmp/vimproc --reporter dot
   - /tmp/vim-themis/bin/themis --runtimepath /tmp/vimproc --exclude ConcurrentProcess --reporter dot