Importing zeta-chain/node from another go module fails

[gartnera]

We need to remove the go-tss and btcd dependencies in the types directories. We should add a CI check that ensures that the project remains importable.

Related to #2796, #959, #2728, #2750

➜  zetacored-rpc go get github.com/zeta-chain/node@042250c34837f95e0f7c2a00b74266428ca76fb8
➜  zetacored-rpc go mod tidy
go: downloading gitlab.com/thorchain/tss/go-tss v1.6.5
go: downloading github.com/gogo/protobuf v1.3.3
go: downloading github.com/hashicorp/go-uuid v1.0.0
go: downloading github.com/klauspost/cpuid v0.0.0-20170728055534-ae7887de9fa5
go: finding module for package github.com/agl/ed25519/edwards25519
go: finding module for package github.com/btcsuite/btcd/btcec
go: finding module for package github.com/agl/ed25519
go: zetacored-rpc imports
	github.com/zeta-chain/node/pkg/rpc imports
	github.com/zeta-chain/node/x/crosschain/types imports
	github.com/btcsuite/btcd/btcec: module github.com/btcsuite/btcd@latest found (v0.24.2), but does not contain package github.com/btcsuite/btcd/btcec
go: zetacored-rpc imports
	github.com/zeta-chain/node/pkg/rpc imports
	github.com/cosmos/cosmos-sdk/types/query imports
	github.com/cosmos/cosmos-sdk/store/types imports
	github.com/confio/ics23/go imports
	github.com/gogo/protobuf/proto: reading github.com/gogo/protobuf/go.mod at revision v1.3.3: unknown revision v1.3.3
go: zetacored-rpc imports
	github.com/zeta-chain/node/pkg/rpc imports
	github.com/cosmos/cosmos-sdk/client/grpc/tmservice imports
	github.com/cosmos/cosmos-sdk/baseapp imports
	github.com/cockroachdb/errors imports
	github.com/cockroachdb/errors/errbase imports
	github.com/gogo/protobuf/types: reading github.com/gogo/protobuf/go.mod at revision v1.3.3: unknown revision v1.3.3
go: zetacored-rpc imports
	github.com/zeta-chain/node/pkg/rpc imports
	github.com/cosmos/cosmos-sdk/client/grpc/tmservice imports
	github.com/cosmos/cosmos-sdk/baseapp imports
	github.com/cockroachdb/errors imports
	github.com/cockroachdb/errors/contexttags imports
	github.com/cockroachdb/errors/errorspb imports
	github.com/gogo/protobuf/gogoproto: reading github.com/gogo/protobuf/go.mod at revision v1.3.3: unknown revision v1.3.3
go: zetacored-rpc imports
	github.com/zeta-chain/node/pkg/rpc imports
	github.com/zeta-chain/node/x/observer/types imports
	gitlab.com/thorchain/tss/go-tss/blame imports
	gitlab.com/thorchain/tss/go-tss/conversion imports
	gitlab.com/thorchain/tss/tss-lib/crypto imports
	github.com/decred/dcrd/dcrec/edwards/v2 imports
	github.com/agl/ed25519: module github.com/agl/ed25519@latest found (v0.0.0-20200225211852-fd4d107ace12), but does not contain package github.com/agl/ed25519
go: zetacored-rpc imports
	github.com/zeta-chain/node/pkg/rpc imports
	github.com/zeta-chain/node/x/observer/types imports
	gitlab.com/thorchain/tss/go-tss/blame imports
	gitlab.com/thorchain/tss/go-tss/conversion imports
	gitlab.com/thorchain/tss/tss-lib/crypto imports
	github.com/decred/dcrd/dcrec/edwards/v2 imports
	github.com/agl/ed25519/edwards25519: module github.com/agl/ed25519@latest found (v0.0.0-20200225211852-fd4d107ace12), but does not contain package github.com/agl/ed25519/edwards25519
go: zetacored-rpc imports
	github.com/zeta-chain/node/pkg/rpc imports
	github.com/cosmos/cosmos-sdk/client tested by
	github.com/cosmos/cosmos-sdk/client.test imports
	github.com/cosmos/cosmos-sdk/runtime imports
	github.com/cosmos/cosmos-sdk/server/api imports
	github.com/cosmos/gogogateway imports
	github.com/gogo/googleapis/google/api imports
	github.com/gogo/protobuf/protoc-gen-gogo/descriptor: reading github.com/gogo/protobuf/go.mod at revision v1.3.3: unknown revision v1.3.3