Add missing import histogram_grouping.html to csv_builder.html.
Add missing import histogram_grouping.html to csv_builder.html.

Currently, running csv_builder_test by itself is broken due to the refactor to
make CSVBuilder use HistogramGroupings.

BUG=catapult:#3507

Review-Url: https://codereview.chromium.org/2985433002

catapult-project/catapult-csm,catapult-project/catapult-csm,catapult-project/catapult-csm,catapult-project/catapult-csm,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult-csm,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult-csm,catapult-project/catapult-csm,catapult-project/catapult