Backport-DOC-7485-2x7 - Remove EoS Support

The Compatibility Matrix in the Mobile docs (https://docs.couchbase.com/sync-gateway/2.7/compatibility-matrix.html) contains Couchbase Server versions that are End of Support i.e 4.x and such entries should be removed.

The reason for such a request is that if an issue with Mobile needs to be investigated form the Server side, we are bound not to do so since the CB Server version is already out of support as per the Support Policy (https://www.couchbase.com/support-policy/enterprise-software).