Random unit test failures with core_message provider testcase

This was noticed on integration testing runs. see here. 

There was 1 failure:

1) core_message_privacy_provider_testcase::test_export_for_context_with_messages

Failed asserting that two strings are equal.

--- Expected

+++ Actual

@@ @@

-'Yes'

+'No'

Looks to be an ordering issue, as it seems $m1, $m2 and $m3 are coming back in the wrong order. Looking at the provider, it does seem to be ordering the messages, so perhaps the issue lies with the get_data call? Not 100% sure.

Additionally, the variables $m7, $m8 and $m9 aren't used in that test and should be removed.

Tagging as all branches in case.