Remove instrumentation for diagnostic messages, forwarding stubs and
covariance, since all this information is present in the expectation
files already.
Change-Id: Idf6622f7eddba801761e13666b470ae6dcc9d59b
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/97106
Reviewed-by: Aske Simon Christensen <askesc@google.com>