**Apache Airflow version**: 2.0.1

**Environment**:

- **Cloud provider or hardware configuration**: docker container
- **OS** (e.g. from /etc/os-release): `Debian GNU/Linux 10 (buster)`
- **Kernel** (e.g. `uname -a`): `Linux 69a18af222ff 3.10.0-1160.15.2.el7.x86_64 #1 SMP Thu Jan 21 16:15:07 EST 2021 x86_64 GNU/Linux`
- **Install tools**: `pip`
- **Others**: `azure` extras

**What happened**:

`airflow.providers.microsoft.azure.hooks.wasb.WasbHook.delete_file` unable to delete blobs if both conditions below are true:

* `is_prefix` argument set to `True`
* the target blobs contain at least one '/' character in their names


**What you expected to happen**:
All files starting with the specified prefix are removed.

The problem is caused by this line: https://github.com/apache/airflow/blob/73187871703bce22783a42db3d3cec9045ee1de2/airflow/providers/microsoft/azure/hooks/wasb.py#L410

By not specifying `delimiter = ''` the listed blobs won't be terminal blobs if the target blobs happen to contain the default delimiter (`/`) in their name

**How to reproduce it**:

For example, consider the following scenario. We have a blob container `cnt` with two files:
* `parent/file1`
* `parent/file2`

The following call should delete both files:
``` python
wasb_hook= WasbHook(...)
wasb_hook.delete_file(
    container_name='cnt',
    blob_name='parent',
    is_prefix=True,
)
```
But instead we get an error `Blob(s) not found: ('parent/',)`


airflow/providers/microsoft/azure/hooks/wasb.py
self,
        container_name,
        blob_name,
        data,
        blob_type: str = 'BlockBlob',
        length: Optional[int] = None,
        **kwargs,
    ) -> Dict[str, Any]:
        """
        Creates a new blob from a data source with automatic chunking.
        :param container_name: The name of the container to upload data
        :type container_name: str
        :param blob_name: The name of the blob to upload. This need not exist in the container
        :type blob_name: str
        :param data: The blob data to upload
        :param blob_type: The type of the blob. This can be either ``BlockBlob``,
            ``PageBlob`` or ``AppendBlob``. The default value is ``BlockBlob``.
        :type blob_type: storage.BlobType
        :param length: Number of bytes to read from the stream. This is optional,
            but should be supplied for optimal performance.
        :type length: int
        """
        blob_client = self._get_blob_client(container_name, blob_name)
        return blob_client.upload_blob(data, blob_type, length=length, **kwargs)
    def download(