Remove govuk from possible brands

‘GOV.UK’ doesn’t make sense as a type of brand. It only made sense as
a type of branding that a service had.

Since we’ve:
- deprecated the service branding column
- made sure it’s not used as a value in the email branding table

we can remove this value from the table of possible brand types.

tests/app/delivery/test_send_to_providers.py

@@ -21,7 +21,6 @@ from app.models import (
     KEY_TYPE_TEST,
     KEY_TYPE_TEAM,
     BRANDING_ORG,
-    BRANDING_GOVUK,
     BRANDING_BOTH,
     BRANDING_ORG_BANNER
 )
@@ -202,7 +201,6 @@ def test_send_sms_should_use_template_version_from_notification_not_latest(
 def test_should_call_send_sms_response_task_if_research_mode(
         notify_db, sample_service, sample_notification, mocker, research_mode, key_type
 ):
-    sample_service.branding = BRANDING_GOVUK
     mocker.patch('app.mmg_client.send_sms')
     mocker.patch('app.delivery.send_to_providers.send_sms_response')
 
@@ -446,15 +444,8 @@ def test_get_html_email_renderer_with_branding_details(branding_type, govuk_bann
 
 
 def test_get_html_email_renderer_with_branding_details_and_render_govuk_banner_only(notify_db, sample_service):
-    email_branding = EmailBranding(
-        brand_type=BRANDING_GOVUK,
-        colour='#000000',
-        logo='justice-league.png',
-        name='Justice League',
-        text='League of Justice',
-    )
-    sample_service.email_branding = email_branding
-    notify_db.session.add_all([sample_service, email_branding])
+    sample_service.email_branding = None
+    notify_db.session.add_all([sample_service])
     notify_db.session.commit()
 
     options = send_to_providers.get_html_email_options(sample_service)