DOC Further 0.22 whats_new cleanup (scikit-learn#15675)

* whats_new cleanup

* fix indent

* reorder hgbt ones

* add Guillaume to contributors and remove unnecessary entry

Author: adrinjalali

doc/whats_new/_contributors.rst

@@ -175,3 +175,5 @@
 .. _Thomas Fan: https://github.com/thomasjpfan
 
 .. _Nicolas Hug: https://github.com/NicolasHug
+
+.. _Guillaume Lemaitre: https://github.com/glemaitre