Cleanup: Get rid of the url and file name members in QQmlCompiledData

This is part of the effor of moving members from QQmlCompiledData into
QV4::CompilationUnit in order to eliminate the former in the long run.

Change-Id: Icce7fe0ee9a49cb3a7677fd7020008fc55ecdcf6
Reviewed-by: Lars Knoll <lars.knoll@digia.com>