Remove needless statement

Changing 'default-tab-width' makes no sense. Only changing 'tab-width'
is enough to changing tab size of buffer.

And 'default-tab-width' causes a byte-compile warning
because it is obsolete variable.
Merge pull request #37 from syohex/remove-ignore-statement

Remove needless statement
Add 'Tests' IMenu entries.
Merge branch 'master' of https://github.com/elixir-lang/emacs-elixir