When `render` was moved from ActionPack to ActionView in acc8e259,
some fixtures required by the tests were duplicated, but they are
actually only required by ActionView tests.

To give one example, `double_render` is already defined [in the AV tests](https://github.com/rails/rails/blob/72139d8d310d896db78eaec98582c7a638135102/actionview/test/actionpack/controller/render_test.rb#L407)
and is never used in the ActionPack tests.