ContextDataFetcherDecorator removes TrivialDataFetcher hint

[osi]

when the ContextDataFetcherDecorator runs to decorate all defined data fetchers in the code registry, it stomps over the TrivialDataFetcher marker.

it should either:

• preserve the marker, so the data fetchers do not get instrumentation applied
• have a policy of not decorating trivial data fetchers (preserving them as-is)

[rstoyanchev]

Superseded by #983.