Remove optional type="JavaScript" from script tags

http://www.whatwg.org/specs/web-apps/current-work/#attr-script-type

  The type attribute gives the language of the script or format of the
  data. If the attribute is present, its value must be a valid MIME
  type. The charset parameter must not be specified. The default,
  which is used if the attribute is absent, is "text/javascript"."

Blink is less strict than other browsers. Removing the optional type
attribute enables tests to be run in other browsers, notably Firefox.

BUG=308992
NOTRY=true

Review URL: https://codereview.chromium.org/209333007

git-svn-id: svn://svn.chromium.org/blink/trunk@169872 bbb929c8-8fbe-4397-9dbb-9b2b20218538