Use E for EthSpec globally (#5264)

* Use `E` for `EthSpec` globally

* Fix tests

* Merge branch 'unstable' into e-ethspec

* Merge branch 'unstable' into e-ethspec

# Conflicts:
#	beacon_node/execution_layer/src/engine_api.rs
#	beacon_node/execution_layer/src/engine_api/http.rs
#	beacon_node/execution_layer/src/engine_api/json_structures.rs
#	beacon_node/execution_layer/src/test_utils/handle_rpc.rs
#	beacon_node/store/src/partial_beacon_state.rs
#	consensus/types/src/beacon_block.rs
#	consensus/types/src/beacon_block_body.rs
#	consensus/types/src/beacon_state.rs
#	consensus/types/src/config_and_preset.rs
#	consensus/types/src/execution_payload.rs
#	consensus/types/src/execution_payload_header.rs
#	consensus/types/src/light_client_optimistic_update.rs
#	consensus/types/src/payload.rs
#	lcli/src/parse_ssz.rs

beacon_node/operation_pool/src/attester_slashing.rs

@@ -4,16 +4,16 @@ use std::collections::{HashMap, HashSet};
 use types::{AttesterSlashing, BeaconState, EthSpec};
 
 #[derive(Debug, Clone)]
-pub struct AttesterSlashingMaxCover<'a, T: EthSpec> {
-    slashing: &'a AttesterSlashing<T>,
+pub struct AttesterSlashingMaxCover<'a, E: EthSpec> {
+    slashing: &'a AttesterSlashing<E>,
     effective_balances: HashMap<u64, u64>,
 }
 
-impl<'a, T: EthSpec> AttesterSlashingMaxCover<'a, T> {
+impl<'a, E: EthSpec> AttesterSlashingMaxCover<'a, E> {
     pub fn new(
-        slashing: &'a AttesterSlashing<T>,
+        slashing: &'a AttesterSlashing<E>,
         proposer_slashing_indices: &HashSet<u64>,
-        state: &BeaconState<T>,
+        state: &BeaconState<E>,
     ) -> Option<Self> {
         let mut effective_balances: HashMap<u64, u64> = HashMap::new();
         let epoch = state.current_epoch();
@@ -36,18 +36,18 @@ impl<'a, T: EthSpec> AttesterSlashingMaxCover<'a, T> {
     }
 }
 
-impl<'a, T: EthSpec> MaxCover for AttesterSlashingMaxCover<'a, T> {
+impl<'a, E: EthSpec> MaxCover for AttesterSlashingMaxCover<'a, E> {
     /// The result type, of which we would eventually like a collection of maximal quality.
-    type Object = AttesterSlashing<T>;
-    type Intermediate = AttesterSlashing<T>;
+    type Object = AttesterSlashing<E>;
+    type Intermediate = AttesterSlashing<E>;
     /// The type used to represent sets.
     type Set = HashMap<u64, u64>;
 
-    fn intermediate(&self) -> &AttesterSlashing<T> {
+    fn intermediate(&self) -> &AttesterSlashing<E> {
         self.slashing
     }
 
-    fn convert_to_object(slashing: &AttesterSlashing<T>) -> AttesterSlashing<T> {
+    fn convert_to_object(slashing: &AttesterSlashing<E>) -> AttesterSlashing<E> {
         slashing.clone()
     }
 
@@ -58,7 +58,7 @@ impl<'a, T: EthSpec> MaxCover for AttesterSlashingMaxCover<'a, T> {
     /// Update the set of items covered, for the inclusion of some object in the solution.
     fn update_covering_set(
         &mut self,
-        _best_slashing: &AttesterSlashing<T>,
+        _best_slashing: &AttesterSlashing<E>,
         covered_validator_indices: &HashMap<u64, u64>,
     ) {
         self.effective_balances