**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
"""Returns custom field behaviour"""
        return {
            "hidden_fields": ['schema', 'port', 'host'],
            "relabeling": {
                'login': 'Blob Storage Login (optional)',
                'password': 'Blob Storage Key (optional)',
                'host': 'Account Name (Active Directory Auth)',
            },
            "placeholders": {
                'extra': 'additional options for use with FileService and AzureFileVolume',
                'login': 'account name',
                'password': 'secret',
                'host': 'account url',
                'extra__wasb__connection_string': 'connection string auth',
                'extra__wasb__tenant_id': 'tenant',
                'extra__wasb__shared_access_key': 'shared access key',
                'extra__wasb__sas_token': 'account url or token',
            },
        }
    def __init__(self, wasb_conn_id: str = default_conn_name, public_read: bool = False) -> None: