[API CHANGE] Remove internal-only osl/diagnose.hxx from SDK

...which should ideally have no effect on external code anyway, given it only
contains internal-only code.

Its use of boost/unordered_set.hpp apparently started to cause problems in
combination with C++98-enforcing CppunitTest_odk_checkapi, cf.
<http://lists.freedesktop.org/archives/libreoffice/2014-September/063637.html>
"Re: Performance samples for LibreOffice ..."

Change-Id: I8b5623950330180fb0ae158903ccecedaed57dfe