Remove CGC from data_availability checker (#7033)

- Part of https://github.com/sigp/lighthouse/issues/6767

Validator custody makes the CGC and set of sampling columns dynamic. Right now this information is stored twice:
- in the data availability checker
- in the network globals

If that state becomes dynamic we must make sure it is in sync updating it twice, or guarding it behind a mutex. However, I noted that we don't really have to keep the CGC inside the data availability checker. All consumers can actually read it from the network globals, and we can update `make_available` to read the expected count of data columns from the block.

beacon_node/beacon_chain/tests/payload_invalidation.rs

@@ -21,6 +21,7 @@ use task_executor::ShutdownReason;
 use types::*;
 
 const VALIDATOR_COUNT: usize = 32;
+const CGC: usize = 8;
 
 type E = MainnetEthSpec;
 
@@ -1050,7 +1051,7 @@ async fn invalid_parent() {
 
     // Ensure the block built atop an invalid payload is invalid for gossip.
     assert!(matches!(
-        rig.harness.chain.clone().verify_block_for_gossip(block.clone()).await,
+        rig.harness.chain.clone().verify_block_for_gossip(block.clone(), CGC).await,
         Err(BlockError::ParentExecutionPayloadInvalid { parent_root: invalid_root })
         if invalid_root == parent_root
     ));