**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
#
#
#
#
"""
This module contains integration with Azure Blob Storage.
It communicate via the Window Azure Storage Blob protocol. Make sure that a
Airflow connection of type `wasb` exists. Authorization can be done by supplying a
login (=Storage account name) and password (=KEY), or login and SAS token in the extra
field (see connection `wasb_default` for an example).
"""
from typing import Any, Dict, List, Optional
from azure.core.exceptions import ResourceExistsError, ResourceNotFoundError
from azure.identity import ClientSecretCredential
from azure.storage.blob import BlobClient, BlobServiceClient, ContainerClient, StorageStreamDownloader
from airflow.exceptions import AirflowException
from airflow.hooks.base import BaseHook
class WasbHook(BaseHook):