Remove sphinxcontrib-blockdiag doc dependency

This is because Pillow upgrade to version 10.x
(from OpenStack upper constraints) breaks its usage.

Change-Id: Iec6567df69a5e1468151f1162600ca254a649c23

doc/requirements.txt

@@ -3,6 +3,5 @@
 # process, which may cause wedges in the gate later.
 
 sphinx>=2.0.0,!=2.1.0 # BSD
-sphinxcontrib-blockdiag>=1.1.0
 openstackdocstheme>=2.2.1 # Apache-2.0
 reno>=3.1.0 # Apache-2.0

doc/source/conf.py

@@ -21,7 +21,6 @@ sys.path.insert(0, os.path.abspath('../..'))
 # extensions coming with Sphinx (named 'sphinx.ext.*') or your custom ones.
 extensions = [
     'openstackdocstheme',
-    'sphinxcontrib.blockdiag'
 ]
 
 # openstackdocstheme options

doc/source/devref/fluent-logging.rst

@@ -32,14 +32,6 @@ Elasticsearch indexes the logs in a logstash-* index by default. Kafka stores
 the logs in a ``logs`` topic by default. Any external tool can then consume the
 ``logs`` topic.
 
-.. blockdiag::
-
-   diagram {
-     fluent-bit [stacked];
-     fluent-bit -> fluentd -> elasticsearch -> kibana;
-          fluentd -> kafka -> external_tool;
-   }
-
 The resulting logs can then be queried directly through Elasticsearch, or they
 can be viewed via Kibana. Kibana offers a dashboard that can create custom views
 on logged events, and Kibana integrates well with Elasticsearch by default.