remove file_content and make expires_at not required

dbschema/default.gel

@@ -4,14 +4,13 @@ module default {
   type files {
     required file_id: str;
     required file_name: str;
-    property file_content: str;
     required file_size: str;
     required note: str;
 
     required content_type: str {
       readonly := true;
     }
-    required expires_at: datetime;
+    property expires_at: datetime;
     required uploaded_at: datetime {
       readonly := true;
     }