remove reference to calendar1 css

it doesn't exist and is not used anyway

this fixes this warning:
Jammit Warning: No assets match 'public/stylesheets_compiled/k12_high_contrast/pages/calendar/calendar.css'

test plan:
run rake canvas:compile_assets and see that you
don't get that warning

Change-Id: I547b846e922139d3cd7580e6c121ca53f131a9b4
Reviewed-on: https://gerrit.instructure.com/38483
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Colleen Palmer <colleen@instructure.com>
Product-Review: Ryan Shaw <ryan@instructure.com>
QA-Review: Ryan Shaw <ryan@instructure.com>