**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 connection widgets to add to connection form"""
        from flask_appbuilder.fieldwidgets import BS3PasswordFieldWidget, BS3TextFieldWidget
        from flask_babel import lazy_gettext
        from wtforms import PasswordField, StringField
        return {
            "extra__wasb__connection_string": PasswordField(
                lazy_gettext('Blob Storage Connection String (optional)'), widget=BS3PasswordFieldWidget()
            ),
            "extra__wasb__shared_access_key": PasswordField(
                lazy_gettext('Blob Storage Shared Access Key (optional)'), widget=BS3PasswordFieldWidget()
            ),
            "extra__wasb__tenant_id": StringField(
                lazy_gettext('Tenant Id (Active Directory Auth)'), widget=BS3TextFieldWidget()
            ),
            "extra__wasb__sas_token": PasswordField(
                lazy_gettext('SAS Token (optional)'), widget=BS3PasswordFieldWidget()
            ),
        }
    @staticmethod
    def get_ui_field_behaviour() -> Dict: