**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
hook = WasbHook(wasb_conn_id=self.shared_key_conn_id)
        hook._get_blob_client(container_name='mycontainer', blob_name='myblob')
        mock_instance = mock_service.return_value.get_container_client
        mock_instance.assert_called_once_with('mycontainer')
        mock_instance.return_value.get_blob_client.assert_called_once_with('myblob')
    @mock.patch("airflow.providers.microsoft.azure.hooks.wasb.BlobServiceClient")
    def test_create_container(self, mock_service):
        hook = WasbHook(wasb_conn_id=self.shared_key_conn_id)
        hook.create_container(container_name='mycontainer')
        mock_instance = mock_service.return_value.get_container_client
        mock_instance.assert_called_once_with('mycontainer')
        mock_instance.return_value.create_container.assert_called()
    @mock.patch("airflow.providers.microsoft.azure.hooks.wasb.BlobServiceClient")
    def test_delete_container(self, mock_service):
        hook = WasbHook(wasb_conn_id=self.shared_key_conn_id)
        hook.delete_container('mycontainer')
        mock_service.return_value.get_container_client.assert_called_once_with('mycontainer')
        mock_service.return_value.get_container_client.return_value.delete_container.assert_called()
    @mock.patch("airflow.providers.microsoft.azure.hooks.wasb.BlobServiceClient")
    @mock.patch.object(WasbHook, 'delete_blobs')
    def test_delete_single_blob(self, delete_blobs, mock_service):
        hook = WasbHook(wasb_conn_id=self.shared_key_conn_id)
        hook.delete_file('container', 'blob', is_prefix=False)
        delete_blobs.assert_called_once_with('container', 'blob')
    @mock.patch.object(WasbHook, 'delete_blobs')
    @mock.patch.object(WasbHook, 'get_blobs_list')
    @mock.patch.object(WasbHook, 'check_for_blob')
    def test_delete_multiple_blobs(self, mock_check, mock_get_blobslist, mock_delete_blobs):