We assume (and check for in configure) 4.2 or later now. In reality
all of the removed checks are for far older versions.

FMT_ioreq_size is no longer needed.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Reviewed-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>