refactor(tvix/store/blobsvc): drop Result<_,_> around open_write

We never returned Err here anyways, and we can still return an error
during the first (or subsequent) write(s).

Change-Id: I4b4cd3d35f6ea008e9ffe2f7b71bfc9187309e2f
Reviewed-on: https://cl.tvl.fyi/c/depot/+/8750
Autosubmit: flokli <flokli@flokli.de>
Tested-by: BuildkiteCI
Reviewed-by: tazjin <tazjin@tvl.su>

tvix/store/src/blobservice/sled.rs

@@ -46,8 +46,8 @@ impl BlobService for SledBlobService {
     }
 
     #[instrument(skip(self))]
-    fn open_write(&self) -> Result<Box<dyn BlobWriter>, Error> {
-        Ok(Box::new(SledBlobWriter::new(self.db.clone())))
+    fn open_write(&self) -> Box<dyn BlobWriter> {
+        Box::new(SledBlobWriter::new(self.db.clone()))
     }
 }