quic: fixup linting issue after other changes

Signed-off-by: James M Snell <jasnell@gmail.com>

Author: jasnell

src/quic/endpoint.cc

@@ -29,7 +29,6 @@ namespace node {
 
 using v8::Array;
 using v8::ArrayBufferView;
-using v8::BackingStore;
 using v8::HandleScope;
 using v8::Integer;
 using v8::Just;