iomap: drop me [hch] from MAINTAINERS for iomap

As Darrick prefers to micro-manage this without looking at my input
for code I wrote and then complain about getting burned out by that
I might as well drop myself from the maintainers file.

[djwong: and I don't like it when you all bikeshed a single-patch
submission to the point that new bugs are being introduced in the scope
creep that wasn't part of V1-V7!]

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>