cros_vm_constants: remove obsolete constants

No CS hits for VMDK, VMX, VBOX constants. Last use of DEFAULT_MEM has
also just been removed now that image_to_vm.sh recommends using cros_vm.

BUG=chromium:782664
TEST=Looked up CS, Pre-CQ and CQ should confirm.

Change-Id: Iaedd835c99db0033b6b72e606aa1225531fdd353
Reviewed-on: https://chromium-review.googlesource.com/889409
Commit-Ready: Nicolas Norvez <norvez@chromium.org>
Tested-by: Nicolas Norvez <norvez@chromium.org>
Reviewed-by: Achuith Bhandarkar <achuith@chromium.org>
1 file changed