Remove unnecessary plan updates in the IntentResource Update method

[ctjnkns]

This may be unnecessary.

Is anything other than the timestamp subject to change? Update the timestamp and commit the state. Your comment references values which must be retrieved, but here's the thing: if they're not part of the config/plan, the Update() method will never run, so those values will be out-of-date in the terraform state until a configurable value is changed. If you think users might rely on these read-only (computed) attributes, it's better to make them available via a data source (always current!) than to consume them via a resource which may become stale.