Revert "radix tree test suite: fix compilation"

This reverts commit 53855d10.

It shouldn't have come in yet - it depends on the changes in linux-next
that will come in during the next merge window.  As Matthew Wilcox says,
the test suite is broken with the current state without the revert.

Requested-by: Matthew Wilcox <mawilcox@microsoft.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>