Remove RaisesException from getCurrentPosition and watchPosition

According to Geolocation API specification getCurrentPosition and
watchPosition does not raise exception, and current RaisesException
for them in the Geolocation.idl are meaningless Because it never
affect to generating bindings codes at all. Therefore we do not
need to keep them in that idl.

BUG=368184

Review URL: https://codereview.chromium.org/297353002

git-svn-id: svn://svn.chromium.org/blink/trunk@175133 bbb929c8-8fbe-4397-9dbb-9b2b20218538