Revert "Add `subscription` to Channel"

This reverts commit 80407f9335e959e84d5d5a3f3cb08a67cf89ccdf.
Revert "Add `subscribed_channels` to Channel"

This reverts commit bdc09f916ba2da4a3cd7cb8b89f9a2956dcce6e9.
Revert "Add `subscribers` to Account"

This reverts commit 2b3576ed91af1164219b53b7384c6ecff52cccd6.
Merge branch 'revert-better-subscription-taxonomy'