doc: remove superfluous warning

We have been using Sphinx >=3 since 2020. We don't expect issues.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
diff --git a/doc/conf.py b/doc/conf.py
index 3db70f8..00f2413 100644
--- a/doc/conf.py
+++ b/doc/conf.py
@@ -47,10 +47,6 @@
 # the process to proceed; hopefully somebody will fix this properly soon.
 #
 if major >= 3:
-    sys.stderr.write('''WARNING: The kernel documentation build process
-        support for Sphinx v3.0 and above is brand new. Be prepared for
-        possible issues in the generated output.
-        ''')
     if (major > 3) or (minor > 0 or patch >= 2):
         # Sphinx c function parser is more pedantic with regards to type
         # checking. Due to that, having macros at c:function cause problems.