docs: Remove 'role' from 'PROBLEM_AUTHOR' and 'CONTEST_AUTHOR'

Author: utilForever

assets/database.mmd

@@ -73,7 +73,6 @@ erDiagram
     PROBLEM_AUTHOR {
         int problem_id FK
         int user_id FK
-        string role "setter/editor/tester"
     }
     USER ||--o{ PROBLEM_AUTHOR : ""
     PROBLEM ||--o{ PROBLEM_AUTHOR : ""
@@ -100,7 +99,6 @@ erDiagram
     CONTEST_AUTHOR {
         int contest_id FK
         int user_id FK
-        string role "coordinator/tester"
     }
     USER    ||--o{ CONTEST_AUTHOR  : ""
     CONTEST ||--o{ CONTEST_AUTHOR  : ""