revert [skip ci]

Author: takenori-y

docs/source/index.rst

@@ -12,7 +12,6 @@ and Hashimoto laboratory.
     Modules <modules/index>
     Signals <signals>
     Utils <utils>
-    Versions <versions>
 
 - :doc:`Modules <modules/index>`
 - :doc:`Signals <signals>`
@@ -22,4 +21,3 @@ References
 ----------
 
 - :ref:`genindex`
-- :doc:`Previous Versions <versions>`