virDomainCheckpointRedefineCommit: Don't check ABI of definition in checkpoint

virDomainCheckpointRedefineCommit: Don't check ABI of definition in checkpoint

Checking the definition ABI when redefining checkpoints doesn't make
much sense for the following reasons:

* the domain definition in the checkpoint is mostly unused (a relic
  adopted from the snapshot code)

* can be very easily overridden by deleting the checkpoint metadata
  before redefinition

Rather than complicating the logic when we'll be taking into account
that the domain definition may be missing, let's just remove the check.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Daniel Henrique Barboza <danielhb413@gmail.com>