build(deps): remove py35-related constraints

as we no longer support that version of Python.

requirements/constraints.txt

@@ -13,17 +13,5 @@
  
 # TODO: Many pinned dependencies should be unpinned and/or moved to this constraints file.
 
-# mock version 4.0.0 drops support for python 3.5
-mock<4.0.0
-
-# Zip > 1.2.0 drops support for python 3.5
-zipp<1.2.0
-
-# Newer versions not available in python 3.5
-stevedore<=1.32.0
-
 # Same as in edx-platform
 djangorestframework==3.9.4
-
-# jsonfield2 3.1.0 drops support for python 3.5
-jsonfield2<3.1.0