Remove spake2_plain authentication method.

remoting/protocol/negotiating_client_authenticator.cc

Index: remoting/protocol/negotiating_client_authenticator.cc
diff --git a/remoting/protocol/negotiating_client_authenticator.cc b/remoting/protocol/negotiating_client_authenticator.cc
index d82312e37a627d7e75df475ca530f56bb2e09098..ab4bd777495c5652f56480bdd1d4c7d0bec3ac0b 100644
--- a/remoting/protocol/negotiating_client_authenticator.cc
+++ b/remoting/protocol/negotiating_client_authenticator.cc
@@ -41,8 +41,6 @@ NegotiatingClientAuthenticator::NegotiatingClientAuthenticator(
 
   AddMethod(Method::SHARED_SECRET_SPAKE2_CURVE25519);
   AddMethod(Method::SHARED_SECRET_SPAKE2_P224);
-
-  AddMethod(Method::SHARED_SECRET_PLAIN_SPAKE2_P224);
 }
 
 NegotiatingClientAuthenticator::~NegotiatingClientAuthenticator() {}
@@ -164,7 +162,6 @@ void NegotiatingClientAuthenticator::CreateAuthenticatorForCurrentMethod(
       break;
     }
 
-    case Method::SHARED_SECRET_PLAIN_SPAKE2_P224:
     case Method::SHARED_SECRET_SPAKE2_P224:
     case Method::SHARED_SECRET_SPAKE2_CURVE25519:
       config_.fetch_secret_callback.Run(
@@ -195,10 +192,7 @@ void NegotiatingClientAuthenticator::CreateSharedSecretAuthenticator(
     const base::Closure& resume_callback,
     const std::string& shared_secret) {
   std::string shared_secret_hash =
-      (current_method_ == Method::SHARED_SECRET_PLAIN_SPAKE2_P224)
-          ? shared_secret
-          : GetSharedSecretHash(config_.host_id, shared_secret);
-
+      GetSharedSecretHash(config_.host_id, shared_secret);
   if (current_method_ == Method::SHARED_SECRET_SPAKE2_CURVE25519) {
     current_authenticator_ = Spake2Authenticator::CreateForClient(
         local_id_, remote_id_, shared_secret_hash, initial_state);