Revert the wxDataObjectComposite checks added by r58549.

Revert the wxDataObjectComposite checks added by r58549.

The checks for data format duplication in wxDataObjectComposite::Add() added
by this revision were broken and didn't actually check anything. It also
doesn't seem clear why do we need them at all so simply remove them. See #10437
for more details.

This also closes #12113 as a side effect because the messages are not present
any more.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@64933 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775