Remove unused exception parameter from biggrep/indexer/BentoNotebookTool.cpp

Summary:
`-Wunused-exception-parameter` has identified an unused exception parameter. This diff removes it.

This:
```
try {
    ...
} catch (exception& e) {
    // no use of e
}
```
should instead be written as
```
} catch (exception&) {
```

If the code compiles, this is safe to land.

Reviewed By: palmje

Differential Revision: D55092140

fbshipit-source-id: 1ff2ddd032a23c220b89a6b90f1d50a06a37f412

Author: r-barnes

cachelib/cachebench/cache/Cache-inl.h

@@ -131,7 +131,7 @@ Cache<Allocator>::Cache(const CacheConfig& config,
         if (!isDir) {
           isBlk = cachelib::util::isBlk(path);
         }
-      } catch (const std::system_error& e) {
+      } catch (const std::system_error&) {
         XLOGF(INFO, "nvmCachePath {} does not exist", path);
         isDir = false;
       }