Un-deprecate test utils functions such as extend_chain (#4255)

## Issue Addressed

This PR un-deprecates some commonly used test util functions, e.g. `extend_chain`. Most of these were deprecated in 2020 but some of us still found them quite convenient and they're still being used a lot. If there's no issue with using them, I think we should remove the "Deprecated" comment to avoid confusion.

beacon_node/beacon_chain/src/test_utils.rs

@@ -83,7 +83,7 @@ pub type AddBlocksResult<E> = (
     BeaconState<E>,
 );
 
-/// Deprecated: Indicates how the `BeaconChainHarness` should produce blocks.
+/// Indicates how the `BeaconChainHarness` should produce blocks.
 #[derive(Clone, Copy, Debug)]
 pub enum BlockStrategy {
     /// Produce blocks upon the canonical head (normal case).
@@ -99,7 +99,7 @@ pub enum BlockStrategy {
     },
 }
 
-/// Deprecated: Indicates how the `BeaconChainHarness` should produce attestations.
+/// Indicates how the `BeaconChainHarness` should produce attestations.
 #[derive(Clone, Debug)]
 pub enum AttestationStrategy {
     /// All validators attest to whichever block the `BeaconChainHarness` has produced.
@@ -732,6 +732,7 @@ where
         state.get_block_root(slot).unwrap() == state.get_block_root(slot - 1).unwrap()
     }
 
+    /// Returns a newly created block, signed by the proposer for the given slot.
     pub async fn make_block(
         &self,
         mut state: BeaconState<E>,
@@ -1095,8 +1096,6 @@ where
             .collect()
     }
 
-    /// Deprecated: Use make_unaggregated_attestations() instead.
-    ///
     /// A list of attestations for each committee for the given slot.
     ///
     /// The first layer of the Vec is organised per committee. For example, if the return value is
@@ -2001,9 +2000,6 @@ where
             .collect()
     }
 
-    /// Deprecated: Do not modify the slot clock manually; rely on add_attested_blocks_at_slots()
-    ///             instead
-    ///
     /// Advance the slot of the `BeaconChain`.
     ///
     /// Does not produce blocks or attestations.
@@ -2017,18 +2013,6 @@ where
         self.chain.slot_clock.set_current_time(time);
     }
 
-    /// Deprecated: Use make_block() instead
-    ///
-    /// Returns a newly created block, signed by the proposer for the given slot.
-    pub async fn build_block(
-        &self,
-        state: BeaconState<E>,
-        slot: Slot,
-        _block_strategy: BlockStrategy,
-    ) -> (SignedBeaconBlock<E>, BeaconState<E>) {
-        self.make_block(state, slot).await
-    }
-
     /// Uses `Self::extend_chain` to build the chain out to the `target_slot`.
     pub async fn extend_to_slot(&self, target_slot: Slot) -> Hash256 {
         if self.chain.slot().unwrap() == self.chain.canonical_head.cached_head().head_slot() {
@@ -2064,8 +2048,6 @@ where
         .await
     }
 
-    /// Deprecated: Use add_attested_blocks_at_slots() instead
-    ///
     /// Extend the `BeaconChain` with some blocks and attestations. Returns the root of the
     /// last-produced block (the head of the chain).
     ///