archive: Use access_web_public_stream helper.
archive: Use access_web_public_stream helper.

This is just a refactor to delete potentially security-sensitive
duplicated code.

kou/zulip,rht/zulip,hackerkid/zulip,hackerkid/zulip,hackerkid/zulip,punchagan/zulip,eeshangarg/zulip,hackerkid/zulip,eeshangarg/zulip,punchagan/zulip,zulip/zulip,andersk/zulip,punchagan/zulip,zulip/zulip,zulip/zulip,eeshangarg/zulip,rht/zulip,andersk/zulip,eeshangarg/zulip,eeshangarg/zulip,hackerkid/zulip,kou/zulip,rht/zulip,punchagan/zulip,punchagan/zulip,andersk/zulip,rht/zulip,hackerkid/zulip,zulip/zulip,zulip/zulip,kou/zulip,andersk/zulip,andersk/zulip,kou/zulip,punchagan/zulip,kou/zulip,andersk/zulip,kou/zulip,eeshangarg/zulip,andersk/zulip,rht/zulip,rht/zulip,zulip/zulip,punchagan/zulip,hackerkid/zulip,eeshangarg/zulip,rht/zulip,zulip/zulip,kou/zulip