**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, offset: Optional[int] = None, length: Optional[int] = None, **kwargs
    ) -> StorageStreamDownloader:
        """
        Downloads a blob to the StorageStreamDownloader
        :param container_name: The name of the container containing the blob
        :type container_name: str
        :param blob_name: The name of the blob to download
        :type blob_name: str
        :param offset: Start of byte range to use for downloading a section of the blob.
            Must be set if length is provided.
        :type offset: int
        :param length: Number of bytes to read from the stream.
        :type length: int
        """
        blob_client = self._get_blob_client(container_name, blob_name)
        return blob_client.download_blob(offset=offset, length=length, **kwargs)
    def create_container(self, container_name: str) -> ContainerClient: