go.crypto: revert 7f5a59ff6b43.

This change reverts https://golang.org/cl/10113043/ because
some folks are stuck on 1.0 till 1.1.1 comes out.

R=golang-dev
CC=golang-dev
https://golang.org/cl/10151043

openpgp/keys.go

@@ -250,6 +250,8 @@ func readToNextPublicKey(packets *packet.Reader) (err error) {
 			return
 		}
 	}
+
+	panic("unreachable")
 }
 
 // ReadEntity reads an entity (public key, identities, subkeys etc) from the

openpgp/packet/packet.go

@@ -272,6 +272,8 @@ func consumeAll(r io.Reader) (n int64, err error) {
 			return
 		}
 	}
+
+	panic("unreachable")
 }
 
 // packetType represents the numeric ids of the different OpenPGP packet types. See

openpgp/packet/public_key.go

@@ -318,6 +318,7 @@ func (pk *PublicKey) VerifySignature(signed hash.Hash, sig *Signature) (err erro
 	default:
 		panic("shouldn't happen")
 	}
+	panic("unreachable")
 }
 
 // keySignatureHash returns a Hash of the message that needs to be signed for