Remove the deprecated ValueSerializer::ReadHeader overload with no context parameter.

src/api.cc

Index: src/api.cc
diff --git a/src/api.cc b/src/api.cc
index 838f52f8032d092f49b1d06afd18638b9e9f9800..ca0c59bab9dfe7e3a45c5be273b965b2c4c40720 100644
--- a/src/api.cc
+++ b/src/api.cc
@@ -3099,11 +3099,6 @@ Maybe<bool> ValueDeserializer::ReadHeader(Local<Context> context) {
   return Just(true);
 }
 
-Maybe<bool> ValueDeserializer::ReadHeader() {
-  Isolate* isolate = reinterpret_cast<Isolate*>(private_->isolate);
-  return ReadHeader(isolate->GetEnteredContext());
-}
-
 void ValueDeserializer::SetSupportsLegacyWireFormat(
     bool supports_legacy_wire_format) {
   private_->supports_legacy_wire_format = supports_legacy_wire_format;