Revert "merge_tree: support existing version numbers"
Revert "merge_tree: support existing version numbers"

This reverts commit 7aa8ca67eb8c95a746501e7fd333320016477607.

Existing versions should not be blindly accepted by overwriting
the version with a new one. Let the adapter be responsible for the
right or no version number on new items.

Netsend/persdb,Netsend/PerspectiveDB,Netsend/PerspectiveDB,Netsend/persdb,Netsend/persdb,Netsend/PerspectiveDB