Bug fix for status overridden by Status::NotFound in db_impl_readonly (#7972)

Summary:
Bug fix for status returned being overridden by Status::NotFound in
DBImpl::OpenForReadOnlyCheckExistence. This was casuing some service
owners to misinterpret the actual error and take appropriate steps.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/7972

Reviewed By: riversand963

Differential Revision: D26499598

Pulled By: akankshamahajan15

fbshipit-source-id: 05e9fedbe2a2e0e53135760f8ff578a2816d2b8e

db/db_impl/db_impl_readonly.cc

@@ -143,9 +143,6 @@ Status OpenForReadOnlyCheckExistence(const DBOptions& db_options,
     uint64_t manifest_file_number;
     s = VersionSet::GetCurrentManifestPath(dbname, fs.get(), &manifest_path,
                                            &manifest_file_number);
-    if (!s.ok()) {
-      return Status::NotFound(CurrentFileName(dbname), "does not exist");
-    }
   }
   return s;
 }