Revert the change to csv filename and make it overwrite any existing file

Reverted commit 80e51e8

(cherry picked from commit cbd2474)

Author: frode-aarstad

src/everest/everest_storage.py

@@ -1186,33 +1186,7 @@ def _sort_df(df: pl.DataFrame, index: list[str]) -> pl.DataFrame:
         )
 
     def export_everest_opt_results_to_csv(self) -> Path:
-        batches_with_data = ",".join(
-            {str(b.batch_id) for b in self.data.batches if b.has_data}
-        )
-        full_path = (
-            self._output_dir
-            / f"experiment_results_batches::{','.join(batches_with_data)}.csv"
-        )
-
-        # Find old csv to delete
-        existing_csv = next(
-            (
-                Path(f)
-                for f in os.listdir(self._output_dir)
-                if f.startswith("experiment_results_batches::")
-            ),
-            None,
-        )
-
-        if (
-            existing_csv is not None
-            and existing_csv.exists()
-            and (self._output_dir / existing_csv) != full_path
-        ):
-            # New batches are added -> overwrite existing csv
-            os.remove(existing_csv)
-
-        if not os.path.exists(full_path):
-            combined_df, _, _ = self.export_dataframes()
-            combined_df.write_csv(full_path)
+        full_path = self._output_dir / "experiment_results.csv"
+        combined_df, _, _ = self.export_dataframes()
+        combined_df.write_csv(full_path)
         return full_path