export: Remove paranoid assertion.
export: Remove paranoid assertion.

There are tactical reasons to remove this assertion.

Basically, the reason it's safe to remove is that it's
been around a long time and we would have seen this
operationally. Also, the check to make sure that the
S3 filename thingy matches the avatar hash is a much
stronger check.

We will soon restore a stronger version of this check
that applies to all of our asset types (emojis/avatars/etc.).

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