Remove hippo:branchInfo mixin when restoring a version

The VersionRestoreToTask is used to restore a version from history. It does this by deleting all child nodes and properties from the target node and then selectively copying them back from the version node. Mixins on the target node however, are not deleted.
This can cause problems if the mixin requires mandatory properties that the version node does not have.

An example is the hippo:branchInfo mixin.
So, at least for this mixin make sure that it is removed before the version node properties are copied back and the session is saved.