Minor cleanup

Author: SimonHeybrock

src/ess/livedata/dashboard/temporal_buffer_manager.py

@@ -129,9 +129,6 @@ def add_extractor(self, key: K, extractor: UpdateExtractor) -> None:
         extractor:
             New extractor that will use this buffer.
         """
-        if key not in self._states:
-            raise KeyError(f"No buffer found for key {key}")
-
         state = self._states[key]
         state.extractors.append(extractor)