Common: remove polymorphic fields from bad rows schemas

[istreeter]

Some of the bad rows schemas contain "polymorphic" fields, e.g. the field value can be an object or a string, depending on the context. This causes problems for querying the badrows in BigQuery, where fields must have a single well-defined type.

The schemas should be simplified so that each field has only one type.

Here is a list of the affected fields:

• Enrichment failures: data.failure.message.error
• Loader iglu error: data.failure.dataReports.targets
• Loader recovery error: data.failure.error.location
• Schema violations: data.failure.messages.error
• Tracker protocol violations: data.failure.messages.error

[istreeter]

See relevant ticket in badrows