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because it is obsolete variable.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
IMenu: List ExUnit tests under "Tests".
Merge branch 'imenu-add-test' of github.com:tomterl/emacs-elixir into imenu-add-test