Remove jsdump references post removal

Author: AA-Turner

.flake8

@@ -29,4 +29,3 @@ exclude =
     doc/usage/extensions/example*.py,
 per-file-ignores =
     tests/*: E501
-    sphinx/util/jsdump.py: SIM905

AUTHORS

@@ -93,12 +93,3 @@ Contributors
 * Zac Hatfield-Dodds -- doctest reporting improvements, intersphinx performance
 
 Many thanks for all contributions!
-
-Included software
-=================
-
-There are also a few modules or functions incorporated from other
-authors and projects:
-
-* sphinx.util.jsdump uses the basestring encoding from simplejson,
-  written by Bob Ippolito, released under the MIT license