spectator: Use display: revert for only-visible-to-spectators.
spectator: Use display: revert for only-visible-to-spectators.

Inherit uses the settings of the parent element; we actually want to
just undo the `display: none` we'd set for this CSS property, which is
what revert is for.

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