subscriptions: Fix scrolling of streams list.
subscriptions: Fix scrolling of streams list.

The previous element passed was a simplebar container which calculated
the incorrect height, thus `scroll_util.scroll_element_into_container`
had no effect.

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