GCC: do not delete move constructor of QuicStreamSendBuffer

QuicStreamSendBuffer constructor is implicitely required in the
initialization of the vector of substreams in QuicCryptoStream.
Though clang apparently ignores that, GCC fails to build.

BUG=chromium:819294

Originally submitted by José Dapena Paz <jose.dapena@lge.com> at https://quiche-review.googlesource.com/c/quiche/+/2420

PiperOrigin-RevId: 241800134
Change-Id: I4e3c97d6e5895d85340e8c1b740e6196d9104066
diff --git a/quic/core/quic_stream_send_buffer.h b/quic/core/quic_stream_send_buffer.h
index e34514b..74e9d0d 100644
--- a/quic/core/quic_stream_send_buffer.h
+++ b/quic/core/quic_stream_send_buffer.h
@@ -62,7 +62,7 @@
  public:
   explicit QuicStreamSendBuffer(QuicBufferAllocator* allocator);
   QuicStreamSendBuffer(const QuicStreamSendBuffer& other) = delete;
-  QuicStreamSendBuffer(QuicStreamSendBuffer&& other) = delete;
+  QuicStreamSendBuffer(QuicStreamSendBuffer&& other) = default;
   ~QuicStreamSendBuffer();
 
   // Save |data_length| of data starts at |iov_offset| in |iov| to send buffer.