views: Use context dictionaries in 'mail'

views: Use context dictionaries in 'mail'

Remove the use of PatchworkRequestContext in this view as it is not
required and causes a 'RemovedInDjango110Warning' warning. This
requires the use of 'render', rather than 'render_to_response'. It
also requires adding a 'request' parameter to 'render_to_string' calls
so that the default context processors continue to be passed through.

This removes a context variable that was not used.

Signed-off-by: Stephen Finucane <stephen.finucane@intel.com>
Tested-by: Andy Doan <andy.doan@linaro.org>