Remove references to `COR_PROFILER` that are no longer needed with MSI

[andrewlock]

What does this PR do?

Simplifies the .NET tracer/profiler install instructions

Motivation

After this PR, the MSI sets the COR_PROFILER and CORECLR_PROFILER variables globally, so there's no need to set them manually. Only applies to Windows MSI install option

Preview

https://docs-staging.datadoghq.com/andrew/update-env-vars/profiler/enabling/dotnet https://docs-staging.datadoghq.com/andrew/update-env-vars/tracing/trace_collection/dd_libraries/dotnet-core.md https://docs-staging.datadoghq.com/andrew/update-env-vars/tracing/trace_collection/dd_libraries/dotnet-framework.md

Additional Notes

N/A

Reviewer checklist

• [ ] Review the changed files.
• [ ] Review the URLs listed in the Preview section.
• [ ] Check images for PII
• [ ] Review any mentions of "Contact Datadog support" for internal support documentation.

[github-actions[bot]]

Preview links (active after the build_preview check completes)

Modified Files

• https://docs-staging.datadoghq.com/andrew/update-env-vars/profiler/enabling/dotnet
• https://docs-staging.datadoghq.com/andrew/update-env-vars/tracing/trace_collection/dd_libraries/dotnet-core
• https://docs-staging.datadoghq.com/andrew/update-env-vars/tracing/trace_collection/dd_libraries/dotnet-framework