Fixes #589 - removes IE10 (x) default clear button

Fixes #589 - removes IE10 (x) default clear button.
IE10 adds an (x) to input fields to clear their contents. Since some
fields have a custom (x) added through the .clearable class, this
removes the default (x) on those fields.
Merge pull request #613 from codeforamerica/589-ie-input

Fixes #589 - removes IE10 (x) default clear button