Remove slot from get_indexed_payload_attestation (#4797)

Get PTC members corresponding to the `payload_attestation` by deriving
the slot from the attestation itself

Author: hangleang

specs/gloas/beacon-chain.md

@@ -609,11 +609,12 @@ def get_ptc(state: BeaconState, slot: Slot) -> Vector[ValidatorIndex, PTC_SIZE]:
 
 ```python
 def get_indexed_payload_attestation(
-    state: BeaconState, slot: Slot, payload_attestation: PayloadAttestation
+    state: BeaconState, payload_attestation: PayloadAttestation
 ) -> IndexedPayloadAttestation:
     """
     Return the indexed payload attestation corresponding to ``payload_attestation``.
     """
+    slot = payload_attestation.data.slot
     ptc = get_ptc(state, slot)
     bits = payload_attestation.aggregation_bits
     attesting_indices = [index for i, index in enumerate(ptc) if bits[i]]
@@ -1154,9 +1155,7 @@ def process_payload_attestation(
     # Check that the attestation is for the previous slot
     assert data.slot + 1 == state.slot
     # Verify signature
-    indexed_payload_attestation = get_indexed_payload_attestation(
-        state, data.slot, payload_attestation
-    )
+    indexed_payload_attestation = get_indexed_payload_attestation(state, payload_attestation)
     assert is_valid_indexed_payload_attestation(state, indexed_payload_attestation)
 ```
 

specs/gloas/fork-choice.md

@@ -178,9 +178,7 @@ def notify_ptc_messages(
     if state.slot == 0:
         return
     for payload_attestation in payload_attestations:
-        indexed_payload_attestation = get_indexed_payload_attestation(
-            state, Slot(state.slot - 1), payload_attestation
-        )
+        indexed_payload_attestation = get_indexed_payload_attestation(state, payload_attestation)
         for idx in indexed_payload_attestation.attesting_indices:
             on_payload_attestation_message(
                 store,