Use custom data provider method for "delete_media"

This is not a REST endpoint, so it's better to use a custom method, see
https://marmelab.com/react-admin/DataProviders.html#adding-custom-methods

Change-Id: I256286949e77b998f759f671b2d4e9790f8ca39c

src/i18n/index.d.ts

@@ -87,6 +87,22 @@ interface SynapseTranslationMessages extends TranslationMessages {
       };
     };
   };
+  delete_media: {
+    name: string;
+    fields: {
+      before_ts: string;
+      size_gt: string;
+      keep_profiles: string;
+    };
+    action: {
+      send: string;
+      send_success: string;
+      send_failure: string;
+    };
+    helper: {
+      send: string;
+    };
+  };
   resources: {
     users: {
       name: string;
@@ -252,22 +268,6 @@ interface SynapseTranslationMessages extends TranslationMessages {
         open: string;
       };
     };
-    delete_media: {
-      name: string;
-      fields: {
-        before_ts: string;
-        size_gt: string;
-        keep_profiles: string;
-      };
-      action: {
-        send: string;
-        send_success: string;
-        send_failure: string;
-      };
-      helper: {
-        send: string;
-      };
-    };
     protect_media?: {
       action: {
         create: string;