Remove go-ssz entirely from prysm (#8257)

* Add DepositSigningData

* gaz

* Add to ssz tests

* Rename to DepositMessage

* Remove deprecated comment

* Remove return

* Fixes from review

* Fixes

* Remove some of gossz

* Remove go-ssz entirely

* Remove unneeded file

* Fix runtime with ssztypes

* Add back ssz files

* Fix formatting

* tidy

* Remove go-ssz from static

* tidy again

* Add tests

* Change to sig

* Fix test

* fx

* Fix visiblity

* Revert "Remove unneeded file"

This reverts commit d66fcda929.

Co-authored-by: Raul Jordan <raul@prysmaticlabs.com>
Co-authored-by: Preston Van Loon <preston@prysmaticlabs.com>
Co-authored-by: prylabs-bulldozer[bot] <58059840+prylabs-bulldozer[bot]@users.noreply.github.com>

go.mod

@@ -83,10 +83,8 @@ require (
 	github.com/prestonvanloon/go-recaptcha v0.0.0-20190217191114-0834cef6e8bd
 	github.com/prometheus/client_golang v1.9.0
 	github.com/prometheus/tsdb v0.10.0 // indirect
-	github.com/protolambda/zssz v0.1.5
 	github.com/prysmaticlabs/ethereumapis v0.0.0-20210115110118-c595a4e0c0a5
 	github.com/prysmaticlabs/go-bitfield v0.0.0-20210120104942-c3214972eb2e
-	github.com/prysmaticlabs/go-ssz v0.0.0-20200612203617-6d5c9aa213ae
 	github.com/prysmaticlabs/prombbolt v0.0.0-20200324184628-09789ef63796
 	github.com/rs/cors v1.7.0
 	github.com/schollz/progressbar/v3 v3.3.4
@@ -119,6 +117,7 @@ require (
 	google.golang.org/protobuf v1.25.0
 	gopkg.in/confluentinc/confluent-kafka-go.v1 v1.4.2
 	gopkg.in/d4l3k/messagediff.v1 v1.2.1
+	gopkg.in/errgo.v2 v2.1.0
 	gopkg.in/yaml.v2 v2.4.0
 	k8s.io/api v0.18.3
 	k8s.io/apimachinery v0.18.3