Remove a part of type checking predicates of HTMLInputElement.

Use |type() == InputTypeNames:foo| instead.
These predicates are inconsistent and confusing.

BUG=
TEST=none; No behavior changes.

Review URL: https://codereview.chromium.org/557613002

git-svn-id: svn://svn.chromium.org/blink/trunk@181598 bbb929c8-8fbe-4397-9dbb-9b2b20218538