test_message_dict: Remove clock time assertion.
test_message_dict: Remove clock time assertion.

Clock time checks lead to tests that nondeterministically fail when
the CI container is super slow, and there's no good reason this test
in particular needs to do that sort of test in addition to our
standard database query count check (which is already does).

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