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

watch/src/blockprint/updater.rs

@@ -6,7 +6,7 @@ use log::{debug, error, warn};
 
 const MAX_SIZE_SINGLE_REQUEST_BLOCKPRINT: u64 = 1600;
 
-impl<T: EthSpec> UpdateHandler<T> {
+impl<E: EthSpec> UpdateHandler<E> {
     /// Forward fills the `blockprint` table starting from the entry with the
     /// highest slot.
     ///