test_bitmap: remove user bitmap tests

We can't run the tests for userspace bitmap parsing if set_fs() doesn't
exist, and it is about to go away for x86, powerpc with other major
architectures to follow.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>