Remove newly added deprecated option (#38808)

Author: timotheeguerin

specification/dynatrace/Dynatrace.Management/tspconfig.yaml

@@ -11,7 +11,6 @@ options:
     output-file: "{azure-resource-provider-folder}/{service-name}/{version-status}/{version}/dynatrace.json"
     emit-lro-options: "all"
     examples-dir: "{project-root}/examples"
-    arm-resource-flattening: false
   "@azure-tools/typespec-csharp":
     emitter-output-dir: "{output-dir}/{service-dir}/{namespace}"
     flavor: azure

specification/recoveryservicesbackup/resource-manager/Microsoft.RecoveryServices/RecoveryServicesBackup/tspconfig.yaml

@@ -9,7 +9,6 @@ options:
     azure-resource-provider-folder: "resource-manager"
     output-file: "{version-status}/{version}/bms.json"
     arm-types-dir: "{project-root}/../../../../common-types/resource-management"
-    arm-resource-flattening: false
     emit-lro-options: "all"
   "@azure-tools/typespec-csharp":
     service-dir: "sdk/recoveryservices-backup"