**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/',)`


tests/providers/microsoft/azure/hooks/test_wasb.py
def setUp(self):
        db.merge_conn(Connection(conn_id='wasb_test_key', conn_type='wasb', login='login', password='key'))
        self.connection_type = 'wasb'
        self.connection_string_id = 'azure_test_connection_string'
        self.shared_key_conn_id = 'azure_shared_key_test'
        self.ad_conn_id = 'azure_AD_test'
        self.sas_conn_id = 'sas_token_id'
        self.public_read_conn_id = 'pub_read_id'
        db.merge_conn(
            Connection(
                conn_id=self.public_read_conn_id,
                conn_type=self.connection_type,
                host='https://accountname.blob.core.windows.net',
            )
        )
        db.merge_conn(
            Connection(