src: remove unused context variable in node_serdes

Currently the following compiler warnings is generated:
../src/node_serdes.cc:400:18:
warning: unused variable 'context' [-Wunused-variable]
  Local<Context> context = ctx->env()->context();
                 ^
1 warning generated.

This commit removes the unused variable.

PR-URL: #24713
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Jon Moss <me@jonathanmoss.me>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

src/node_serdes.cc

@@ -397,7 +397,6 @@ void DeserializerContext::ReadUint64(const FunctionCallbackInfo<Value>& args) {
   uint32_t lo = static_cast<uint32_t>(value);
 
   Isolate* isolate = ctx->env()->isolate();
-  Local<Context> context = ctx->env()->context();
 
   Local<Value> ret[] = {
     Integer::NewFromUnsigned(isolate, hi),