Revert "VMX: flush cache when vmentry back to UC guest"

Revert "VMX: flush cache when vmentry back to UC guest"

This reverts commit 86d60e85 as well as one related change from
62652c00 ("VMX: fix cr0.cd handling"), on the basis that all of this
flushing is still insufficient and, while not known to fix anything, is
known to negatively affect performance.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Release-acked-by: George Dunlap <george.dunlap@eu.citrix.com>
Acked-by: Liu Jinsong <jinsong.liu@intel.com>
Acked-by: Eddie Dong <eddie.dong@intel.com>