tests: Simplify test_event_collapsing.
tests: Simplify test_event_collapsing.

We now use update_message_flags instead of
pointer events.

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