Remove DHKey Encodable conformance

Sources/XXClient/Models/DHKey.swift

@@ -10,7 +10,7 @@ public struct DHKey: Equatable {
   public var fingerprint: UInt64
 }
 
-extension DHKey: Codable {
+extension DHKey: Decodable {
   enum CodingKeys: String, CodingKey {
     case value = "Value"
     case fingerprint = "Fingerprint"
@@ -20,8 +20,4 @@ extension DHKey: Codable {
     let data = convertJsonNumberToString(in: data, at: "Value")
     return try JSONDecoder().decode(Self.self, from: data)
   }
-
-  public func encode() throws -> Data {
-    try JSONEncoder().encode(self)
-  }
 }

Tests/XXClientTests/Models/DHKeyTests.swift

@@ -19,10 +19,5 @@ final class DHKeyTests: XCTestCase {
       value: value,
       fingerprint: fingerprint
     ))
-
-    let encodedModel = try model.encode()
-    let decodedModel = try DHKey.decode(encodedModel)
-
-    XCTAssertNoDifference(decodedModel, model)
   }
 }