Remove useless callback layer from Host*Connection

Remove useless callback layer from Host*Connection

[Bug]           Host*Connection classes had redundant callback layer.
[Cause]         N/A
[Solution]      Make Host*Connection objects aware of ZonesManager.
                Remove unneeded callbacks.
[Verification]  For both with and without Dbus:
                  * Build
                  * Run tests
                  * Make sure, that vasum-cli works

Change-Id: I8fd76d279731efdf201e797f2ef7600aed355aaa