Remove Debian 11 Dockerfiles

[mthalman]

Debian 11 was EOL in Aug 2024 so these Dockerfiles should no longer be maintained.

See dotnet/core#9625

[mthalman]

Since Debian 11 is still in LTS support and is continuing to have its Docker Hub images maintained, we'll defer the removal of these Dockerfiles until all consuming repos have migrated off of these images.

• Migrate off of Debian 11 diagnostics#5064
• Migrate off of Debian 11 arcade#15281
• Migrate off of EOL container images aspnetcore#59185
• Migrate off of EOL container images wcf#5701
• Migrate off of EOL container images runtime#110204