[C#] chore: Remove incomplete functions augmentation (#950)

## Linked issues

closes: #949 
## Details

Remove incomplete `functions` augmentation.

Author: singhk97

dotnet/packages/Microsoft.TeamsAI/Microsoft.TeamsAI/AI/Augmentations/AugmentationType.cs

@@ -10,11 +10,6 @@ public enum AugmentationType
         /// </summary>
         None,
 
-        /// <summary>
-        /// Functions
-        /// </summary>
-        Functions,
-
         /// <summary>
         /// Sequence
         /// </summary>

dotnet/packages/Microsoft.TeamsAI/Microsoft.TeamsAI/AI/Augmentations/FunctionsAugmentation.cs

@@ -164,9 +164,6 @@ private PromptTemplate AppendAugmentations(PromptTemplate template)
 
             switch (template.Configuration.Augmentation.Type)
             {
-                case AugmentationType.Functions:
-                    template.Augmentation = new FunctionsAugmentation();
-                    break;
                 case AugmentationType.Monologue:
                     template.Augmentation = new MonologueAugmentation(template.Actions);
                     break;