[master] 31d22d44a release docs: Do not mention Debug logs

[Nils Goroll]

commit 31d22d44a624e133eaba0f69b254e8f752450f41
Author: Nils Goroll <nils.goroll at uplex.de>
Date:   Fri Mar 13 11:08:53 2020 +0100

    release docs: Do not mention Debug logs
    
    As @Dridi rightfully commented via email, the default vsl_mask does not
    contain Debug

diff --git a/doc/sphinx/whats-new/upgrading-6.4.rst b/doc/sphinx/whats-new/upgrading-6.4.rst
index 557f37697..b70da8d23 100644
--- a/doc/sphinx/whats-new/upgrading-6.4.rst
+++ b/doc/sphinx/whats-new/upgrading-6.4.rst
@@ -26,21 +26,18 @@ varnishd
   connection might not have got closed despite the :ref:`ref_param_send_timeout`
   having been reached. HTTP/2 was not affected.
 
-  When :ref:`ref_param_send_timeout` is reached on HTTP/1, the ``MAIN.sc_tx_error``
-  is increased and a ``Debug`` message ``Hit total send timeout, wrote
-  = x/y; not retrying`` is logged.
-
-  .. actually H2 is really quite different and we have a plan to
-     harmonize timeout handling across the board
-
-  Users with long running backend fetches and HTTP/1 clients should
-  watch out for an increase of the ``MAIN.sc_tx_error`` compared to
-  before the deployment and consider increasing
+  When :ref:`ref_param_send_timeout` is reached on HTTP/1, the
+  ``MAIN.sc_tx_error`` is increased. Users with long running backend
+  fetches and HTTP/1 clients should watch out for an increase of that
+  counter compared to before the deployment and consider increasing
   :ref:`ref_param_send_timeout` appropriately.
 
   The timeout can also be set per connection from VCL as
   ``sess.send_timeout``.
 
+  .. actually H2 is really quite different and we have a plan to
+     harmonize timeout handling across the board
+
 Statistics
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