Remove blk_queue_nonrot() autotools check

This autotools check was never needed because we can check for the
existence of QUEUE_FLAG_NONROT in the kernel headers.

Also, the comment in config/kernel-blk-queue-nonrot.m4 is incorrect.
This was a Linux 2.6.28 API change, not a Linux 2.6.27 API change.

Signed-off-by: Richard Yao <ryao@gentoo.org>