Drop the Sentry.OpenTelemetry package

### Description

This is replaced by `Sentry.OpenTelemetry.Exporter`.

Potentially we could phase this out gradually instead:
- https://github.com/getsentry/sentry-dotnet/issues/4932

Then drop it some time in 2027.

Start by reading the referenced issue #4932 to understand whether the package should be removed immediately or phased out. Identify the project and packaging entry points for Sentry.OpenTelemetry, then confirm that the obsolete package is no longer produced or supported while Sentry.OpenTelemetry.Exporter remains available.

Written by the indexing model from the issue text.