[sinttest] Properly handle AbstractSmackSpecificLowLevelIntegrationTest
Subclasses of AbstractSmackSpecificLowLevelIntegrationTest have test
methods with no parameters. This was, after the refactoring in
c5bb15c631d3 ("[sinttest] Add UnconnectedConnectionSource for
low-level tests") not handled properly.
Fixes: c5bb15c631d3 ("[sinttest] Add UnconnectedConnectionSource for low-level tests")
[core] Fix ErrorIQ not showing potential original IQ child
Also delete StanzaIdTest since the test was fundamentally weak and
flawed. It does not work anyway, since TestIQ has a fixed stanza ID.
