Remove nscoder_util

This was upstreamed for iOS, but the code that uses it won't be
upstreamed into chrome/ under the new plan, and it's not clear yet
where it will live. Nothing else is using it.

BUG=None

Review URL: https://codereview.chromium.org/26880005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@228050 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 228050