* Add test that deletes a custom attribute from a class

* just ignore modified MONO_TABLE_TYPEDEF rows in updates

We may want to validate that Parent, Interfaces and Attributes columns
haven't changed, but it's tricky and might be overly restrictive

* simplify pass1 code.

It's just two branches with comments. Remove the `if` entirely

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Co-authored-by: NAleksey Kliger <alklig@microsoft.com>