models: Improve comment description of emoji_code.
models: Improve comment description of emoji_code.

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