**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: str,
        prefix: Optional[str] = None,
        include: Optional[List[str]] = None,
        delimiter: Optional[str] = '/',
        **kwargs,
    ) -> List:
        """
        List blobs in a given container
        :param container_name: The name of the container
        :type container_name: str
        :param prefix: Filters the results to return only blobs whose names
            begin with the specified prefix.
        :type prefix: str
        :param include: Specifies one or more additional datasets to include in the
            response. Options include: ``snapshots``, ``metadata``, ``uncommittedblobs``,
            ``copy`, ``deleted``.
        :type include: List[str]
        :param delimiter: filters objects based on the delimiter (for e.g '.csv')
        :type delimiter: str
        """
        container = self._get_container_client(container_name)
        blob_list = []
        blobs = container.walk_blobs(name_starts_with=prefix, include=include, delimiter=delimiter, **kwargs)
        for blob in blobs:
            blob_list.append(blob.name)
        return blob_list
    def load_file(self, file_path: str, container_name: str, blob_name: str, **kwargs) -> None: