mention: Simplify init_user_group_data using prefetch_related.
mention: Simplify init_user_group_data using prefetch_related.

Signed-off-by: Anders Kaseorg <dfdb7392591db597bc41cf266a9c3bc12a2706e5@zulip.com>

andersk/zulip,kou/zulip,rht/zulip,andersk/zulip,andersk/zulip,zulip/zulip,kou/zulip,andersk/zulip,eeshangarg/zulip,eeshangarg/zulip,zulip/zulip,eeshangarg/zulip,andersk/zulip,zulip/zulip,andersk/zulip,rht/zulip,kou/zulip,zulip/zulip,rht/zulip,kou/zulip,zulip/zulip,rht/zulip,andersk/zulip,zulip/zulip,rht/zulip,rht/zulip,eeshangarg/zulip,rht/zulip,zulip/zulip,eeshangarg/zulip,kou/zulip,eeshangarg/zulip,kou/zulip,kou/zulip,eeshangarg/zulip