Enr fork (#967)

* Start fixing enr-fork-id

* Fix time-until-next-fork logic

* Remove fork crate

Cargo.lock

@@ -234,7 +234,6 @@ dependencies = [
  "eth2_ssz",
  "eth2_ssz_derive",
  "eth2_ssz_types",
- "fork",
  "futures",
  "genesis",
  "integer-sqrt",
@@ -1479,13 +1478,6 @@ version = "0.1.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "00b0228411908ca8685dba7fc2cdd70ec9990a6e753e89b6ac91a84c40fbaf4b"
 
-[[package]]
-name = "fork"
-version = "0.2.0"
-dependencies = [
- "types",
-]
-
 [[package]]
 name = "fuchsia-cprng"
 version = "0.1.1"