CBL doesn't purge channel removals when removal revision already exists in CBL

Lithium has a feature of handling revocation of channel access:

https://docs.google.com/document/d/14gawyt9lcHYUlCh0APUt-7V6M6Kkk0zoXi7GOfYiMLM/edit#heading=h.8yekawi4x61d

however, the feature will mainly focus on purging docs while the docs owner (user) leaves the channel of the docs belong to. 

I have the following scenarios observed in 2.8 (as well as 2.8.x) need to be also covered by Lithium channel access improvement:

1. create a doc on CBL with channels, replicate (continuous=true) the doc to SGW, on CBL remove all channels the doc was assigned, the doc gets auto purged on CBL (currently the doc stay with empty channel data)
2. create a doc on CBL with channels, replicate (continuous=true) the doc to SGW, on SGW remove all channels the doc was assigned, the doc gets auto purged on CBL (currently docs stay with empty channel data)
3. create a doc on SGW with channels, replicate (continuous=true) the doc to CBL, on SGW remove all channels the doc was assigned, the doc gets auto purged on CBL (currently it works expected)
4. create a doc on SGW with channels, replicate (continuous=true) the doc to CBL, on CBL remove all channels the doc was assigned, the doc gets auto purged on CBL (currently docs stay with empty channel data)

Discussed my observations with Adam and Pasin Suriyentrakorn , will confirm if a CBL doc with empty channel should be purged or not.