Removed all disable_forks (#2925)

#2923 

Which issue # does this PR address?
There's a redundant field on the BeaconChain called disabled_forks that was once part of our fork-aware networking (#953) but which is no longer used and could be deleted. so Removed all references to disabled_forks so that the code compiles and git grep disabled_forks returns no results.

## Proposed Changes

Please list or describe the changes introduced by this PR.
Removed all references of disabled_forks


Co-authored-by: Divma <26765164+divagant-martian@users.noreply.github.com>

beacon_node/client/src/config.rs

@@ -58,8 +58,6 @@ pub struct Config {
     /// This is the method used for the 2019 client interop in Canada.
     pub dummy_eth1_backend: bool,
     pub sync_eth1_chain: bool,
-    /// A list of hard-coded forks that will be disabled.
-    pub disabled_forks: Vec<String>,
     /// Graffiti to be inserted everytime we create a block.
     pub graffiti: Graffiti,
     /// When true, automatically monitor validators using the HTTP API.
@@ -98,7 +96,6 @@ impl Default for Config {
             eth1: <_>::default(),
             execution_endpoints: None,
             suggested_fee_recipient: None,
-            disabled_forks: Vec::new(),
             graffiti: Graffiti::default(),
             http_api: <_>::default(),
             http_metrics: <_>::default(),