Remove default sni version

Author: mdaigle

eng/pipelines/dotnet-sqlclient-ci-core.yml

@@ -45,7 +45,7 @@ parameters:
   displayName: |
     Use a specific SNI version from the internal validation feed
   type: string
-  default: 20250225.1.0-Run-109767-Dev
+  default: ''
 
 - name: SNIValidationFeed
   displayName: |