[DML EP] Don't fuse a capability outside the compile call (#13468)
### Description
DML EP was a special EP w.r.t. capability fusion. It used to fuse a
capability outside the IExecutionProvider::Compile() call. But after
recent re-architecture #13131, it is no longer a special case.
### Motivation and Context
Why is this change required? What problem does it solve?
To make DML EP consistent with the ORT design.
- If it fixes an open issue, please link to the issue here. N/A
Co-authored-by: Sumit Agarwal <sumitagarwal@microsoft.com>