Remove python3-sphinx debian dependency

We use a venv for it. We just need python3 to be present.

https://github.com/apache/couchdb/tree/main/src/docs#readme

debian/control.in

diff --git a/debian/control.in b/debian/control.in
index 03437f9..685f5ba 100644
--- a/debian/control.in
+++ b/debian/control.in
@@ -20,8 +20,8 @@
                %SPIDERMONKEY_DEV%,
                lsb-release,
                po-debconf,
-               python3,
-               python3-sphinx
+               python3
+
 Homepage: http://couchdb.apache.org/
 
 Package: couchdb