Revert loop prevention (#4472)

* Provisioner: Only include and sign bitfields on fresh leaves.

polkadot/roadmap/implementers-guide/src/node/availability/availability-distribution.md

@@ -9,7 +9,7 @@ In particular this subsystem is responsible for:
 - Respond to network requests requesting availability data by querying the
   [Availability Store](../utility/availability-store.md).
 - Request chunks from backing validators to put them in the local `Availability
-  Store` whenever we find an occupied core on the chain,
+  Store` whenever we find an occupied core on any fresh leaf,
   this is to ensure availability by at least 2/3+ of all validators, this
   happens after a candidate is backed.
 - Fetch `PoV` from validators, when requested via `FetchPoV` message from

polkadot/roadmap/implementers-guide/src/node/availability/bitfield-signing.md

@@ -22,7 +22,7 @@ Upon receipt of an `ActiveLeavesUpdate`, launch bitfield signing job for each `a
 Localized to a specific relay-parent `r`
 If not running as a validator, do nothing.
 
-- Begin by waiting a fixed period of time so availability distribution has the chance to make candidates available.
+- For each fresh leaf, begin by waiting a fixed period of time so availability distribution has the chance to make candidates available.
 - Determine our validator index `i`, the set of backed candidates pending availability in `r`, and which bit of the bitfield each corresponds to.
 - Start with an empty bitfield. For each bit in the bitfield, if there is a candidate pending availability, query the [Availability Store](../utility/availability-store.md) for whether we have the availability chunk for our validator index. The `OccupiedCore` struct contains the candidate hash so the full candidate does not need to be fetched from runtime.
 - For all chunks we have, set the corresponding bit in the bitfield.