Revert move to Build-Depends-Indep

Unfortunately, the documentation build is too much entangled with the
main build to cleanly separate them.

debian/control

@@ -16,10 +16,10 @@ Build-Depends: debhelper-compat (= 13),
                libuv1-dev (>= 1.10),
                procps [!hurd-any],
                qtbase5-dev <!stage1>,
-               zlib1g-dev
+               zlib1g-dev,
-Build-Depends-Indep: python3-sphinx,
+               python3-sphinx,
-                     python3-sphinxcontrib.qthelp | python3-sphinx (<< 2.0),
+               python3-sphinxcontrib.qthelp | python3-sphinx (<< 2.0),
-                     dh-sequence-sphinxdoc
+               dh-sequence-sphinxdoc
 Rules-Requires-Root: no
 Standards-Version: 4.6.0
 Vcs-Git: https://salsa.debian.org/cmake-team/cmake.git