Revert "Let SSEClient::stop() interrupt a blocked read"

This reverts commit 3744227de2.

Shutting down the socket does not wake a read waiting in WSAPoll on
Windows while the peer stays silent, so stop() still waited out the read
timeout there and the new tests failed. Faster stop() on the other
platforms also let SSEIntegrationTest.ManualStop return while its server
handler still read a local of the test body (stack-use-after-return).
The fix will come back built on a wait that works on every platform.

httplib.h

@@ -4494,10 +4494,6 @@ private:
   std::atomic<bool> connected_{false};
   std::string last_event_id_;
 
-  // Socket of the open stream, for stop() to shut down
-  std::mutex stream_mutex_;
-  socket_t stream_sock_ = INVALID_SOCKET;
-
   // Async support
   std::thread async_thread_;
 };
@@ -5005,20 +5001,6 @@ inline void SSEClient::start_async() {
 
 inline void SSEClient::stop() {
   running_.store(false);
-  {
-    // Ends a blocked read. The loop withdraws the socket under this lock
-    // before closing it, so it is still open here.
-    std::lock_guard<std::mutex> lock(stream_mutex_);
-    if (stream_sock_ != INVALID_SOCKET) {
-#ifdef _WIN32
-      ::shutdown(stream_sock_, SD_BOTH);
-#else
-      // Only the read side, so that the alert TLS sends on the unexpected EOF
-      // does not raise SIGPIPE
-      ::shutdown(stream_sock_, SHUT_RD);
-#endif
-    }
-  }
   client_.stop(); // Cancel any pending operations
   if (async_thread_.joinable()) { async_thread_.join(); }
 }
@@ -5093,7 +5075,6 @@ inline void SSEClient::run_event_loop() {
     // bounded instead of the whole body.
     auto handle = client_.open_stream("GET", path_, {}, request_headers);
     handle.body_reader_.payload_max_length = 0;
-    auto sock = handle.connection_ ? handle.connection_->sock : INVALID_SOCKET;
     stream::Result result{std::move(handle)};
 
     // Connection error handling
@@ -5126,19 +5107,6 @@ inline void SSEClient::run_event_loop() {
       continue;
     }
 
-    // Hand the socket to stop(), unless it has already been called
-    {
-      std::lock_guard<std::mutex> lock(stream_mutex_);
-      if (!running_.load()) { break; }
-      stream_sock_ = sock;
-    }
-
-    // Destroyed before result, so the socket is withdrawn before it is closed
-    detail::scope_exit withdraw_sock([this] {
-      std::lock_guard<std::mutex> lock(stream_mutex_);
-      stream_sock_ = INVALID_SOCKET;
-    });
-
     // Connection successful
     connected_.store(true);
     reconnect_count = 0;