Clear notifications from muted accounts after massive sync

In massive sync we operate an 1000 blocks at a time. Post notifications
are filled by posts indexer, mutes are filled by follow indexer.
If we process a 1000 blocks batch and there's a mute, it will be
processed by the follow indexer, but this won't be seen by the posts
indexer in this batch. This means that the posts notifications will be
generated even for accounts that are muted.
This essentially means that if there is a mute operation in a 1000
blocks batch, notifications for posts from that batch will not get that
mute into account. So it would be possible for users to get
notifications from an accounts they have recently muted.
The fix is to clear any notifications from muted account at the end of
the massive sync.
The issue should not affect live mode, because we process only one block
at a time.