Revert "Add doOnDiscard hook for streaming mode"

This reverts commit 77a562dfee.

As per findings under
https://github.com/reactor/reactor-netty/issues/1746 it looks this
wasn't the issue and isn't required.

spring-web/src/main/java/org/springframework/http/codec/EncoderHttpMessageWriter.java

@@ -141,18 +141,16 @@ public class EncoderHttpMessageWriter<T> implements HttpMessageWriter<T> {
 		}
 
 		if (isStreamingMediaType(contentType)) {
-			return message
-					.writeAndFlushWith(body.map(buffer -> {
-						Hints.touchDataBuffer(buffer, hints, logger);
-						return Mono.just(buffer).doOnDiscard(PooledDataBuffer.class, DataBufferUtils::release);
-					}))
-					.doOnDiscard(PooledDataBuffer.class, DataBufferUtils::release);
+			return message.writeAndFlushWith(body.map(buffer -> {
+				Hints.touchDataBuffer(buffer, hints, logger);
+				return Mono.just(buffer).doOnDiscard(PooledDataBuffer.class, DataBufferUtils::release);
+			}));
 		}
 
 		if (logger.isDebugEnabled()) {
 			body = body.doOnNext(buffer -> Hints.touchDataBuffer(buffer, hints, logger));
 		}
-		return message.writeWith(body).doOnDiscard(PooledDataBuffer.class, DataBufferUtils::release);
+		return message.writeWith(body);
 	}
 
 	@Nullable