Remove qemudDomainSetMaxMemory.

Remove qemudDomainSetMaxMemory.

As previously discussed[1], this patch removes the
qemudDomainSetMaxMemory() function, since it doesn't
work.  This means that instead of getting somewhat
cryptic errors, you will now get:

error: Unable to change MaxMemorySize
error: this function is not supported by the hypervisor: virDomainSetMaxMemory

Which describes the situation perfectly.

[1] https://www.redhat.com/archives/libvir-list/2010-February/msg00928.html

Signed-off-by: Chris Lalancette <clalance@redhat.com>