[nrf fromtree] doc: remove docutils dependency

docutils is a core dependency of Sphinx. It is only used by some of our
custom Sphinx extensions.

Signed-off-by: Gerard Marull-Paretas <[email protected]>

Author: gmarull

scripts/requirements-doc.txt

@@ -1,7 +1,6 @@
 # DOC: used to generate docs
 
 breathe>=4.23.0
-docutils>=0.16
 sphinx>=3.3.0,<3.4.0
 sphinx_rtd_theme>=0.5.2,<1.0
 sphinx-tabs