[C++][FS][Azure] Implement `DeleteFile()` for flat-namespace storage accounts

### Describe the enhancement requested

`AzureFileSystem::DeleteFile` is implemented for storage accounts with Hierarchical Namespace Support enabled (GH-38703), but not for storage accounts that can use only the Blobs API and represent directories with empty directory marker blobs.

This is a child of GH-18014.

### Component(s)

C++