move choices from form to view

so that when updating, you don't have to update two separate places

app/main/forms.py

@@ -1286,10 +1286,5 @@ class TemplateAndFoldersSelectionForm(Form):
 class ClearCacheForm(StripWhitespaceForm):
     model_type = RadioField(
         'What do you want to clear today',
-        choices=[
-            ('user', 'Users'),
-            ('service', 'Services'),
-            ('template', 'Templates')
-        ],
         validators=[DataRequired()]
     )

app/main/views/platform_admin.py

@@ -1,5 +1,6 @@
 import itertools
 import re
+from collections import OrderedDict
 from datetime import datetime
 
 from flask import abort, flash, redirect, render_template, request, url_for
@@ -291,28 +292,34 @@ def platform_admin_letter_validation_preview():
 @user_is_platform_admin
 def clear_cache():
     # note: `service-{uuid}-templates` cache is cleared for both services and templates.
-    CACHE_KEYS = {
-        'user': [
+    CACHE_KEYS = OrderedDict([
+        ('user', [
             'user-????????-????-????-????-????????????',
-        ],
-        'service': [
+        ]),
+        ('service', [
             'has_jobs-????????-????-????-????-????????????',
             'service-????????-????-????-????-????????????',
             'service-????????-????-????-????-????????????-templates',
             'service-????????-????-????-????-????????????-data-retention',
             'service-????????-????-????-????-????????????-template-folders',
-        ],
-        'template': [
+        ]),
+        ('template', [
             'service-????????-????-????-????-????????????-templates',
             'template-????????-????-????-????-????????????-version-*',
             'template-????????-????-????-????-????????????-versions',
-        ],
-        'email_branding': [
+        ]),
+        ('email_branding', [
             'email_branding',
             'email_branding-????????-????-????-????-????????????',
-        ]
-    }
+        ]),
+        ('letter_branding', [
+            'letter_branding',
+            'letter_branding-????????-????-????-????-????????????',
+        ])
+    ])
+
     form = ClearCacheForm()
+    form.model_type.choices = [(key, key.replace('_', ' ').title()) for key in CACHE_KEYS]
 
     if form.validate_on_submit():
         to_delete = form.model_type.data
@@ -321,8 +328,8 @@ def clear_cache():
             redis_client.delete_cache_keys_by_pattern(pattern)
             for pattern in CACHE_KEYS[to_delete]
         )
-
-        flash('Removed {} {} objects from redis'.format(num_deleted, to_delete), category='default')
+        msg = 'Removed {} {} object{} from redis'
+        flash(msg.format(num_deleted, to_delete, 's' if num_deleted != 1 else ''), category='default')
 
     return render_template(
         'views/platform-admin/clear-cache.html',