docs: Update sphinxcontrib-mermaid

Remove a previous workaround and use v0.7.1.

Bug: 376
No-Docs-Update-Reason: Bugfix
Change-Id: I31246fad196842cf199e85c8ada5c35572dc3c6b
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/57180
Pigweed-Auto-Submit: Anthony DiGirolamo <tonymd@google.com>
Commit-Queue: Auto-Submit <auto-submit@pigweed.google.com.iam.gserviceaccount.com>
Reviewed-by: Rob Mohr <mohrr@google.com>
diff --git a/docs/conf.py b/docs/conf.py
index 37d5471..ed3c21e 100644
--- a/docs/conf.py
+++ b/docs/conf.py
@@ -14,15 +14,6 @@
 """Pigweed's Sphinx configuration."""
 
 import sphinx
-import sphinx_rtd_theme
-
-# TODO(pwbug/376): Remove this when this PR is merged:
-# https://github.com/mgaitan/sphinxcontrib-mermaid/pull/71
-# Needed for sphinxcontrib-mermaid compatibility with sphinx 4.0.0.
-if sphinx.version_info[0] >= 4:
-    import errno
-    import sphinx.util.osutil
-    sphinx.util.osutil.ENOENT = errno.ENOENT
 
 # The suffix of source filenames.
 source_suffix = ['.rst']
diff --git a/pw_docgen/py/setup.py b/pw_docgen/py/setup.py
index c7afefb..8fce765 100644
--- a/pw_docgen/py/setup.py
+++ b/pw_docgen/py/setup.py
@@ -34,6 +34,6 @@
         'sphinxcontrib-blockdiag',
         'sphinxcontrib-nwdiag',
         'sphinxcontrib-seqdiag',
-        'sphinxcontrib-mermaid',
+        'sphinxcontrib-mermaid >=0.7.1',
     ],
 )