Remove unused function

Author: Ariouz

graalpython/com.oracle.graal.python.test/src/runner.py

@@ -1237,9 +1237,7 @@ def without_keys(self, keys: set[str]) -> 'Tag | None':
                 return self
             return Tag(self.test_id, keys, is_exclusion=self.is_exclusion)
 
-    def is_platform_excluded(self, key: str) -> bool:
-        return key not in self.keys
-        
+
     def __str__(self):
         s = ''
         if self.is_exclusion: