gear_menu: Fix obsolete comment about window.onhashchange.
gear_menu: Fix obsolete comment about window.onhashchange.

Commit 0c80fc6abaa67027480538188d38230683211caa (#12737) stopped using
the old-style window.onhashchange property.

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

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