Ensure delete[] and not delete is used on buffer_ (#4647)

Summary:
Ensure delete[] and not delete is called on buffer_, as it is reset with new char[buffer_size_].
Pull Request resolved: https://github.com/facebook/rocksdb/pull/4647

Differential Revision: D12961327

Pulled By: ajkr

fbshipit-source-id: c1af373b98359edfdc291caebe4e0acdfb8afdd8

utilities/blob_db/blob_dump_tool.h

@@ -33,7 +33,7 @@ class BlobDumpTool {
 
  private:
   std::unique_ptr<RandomAccessFileReader> reader_;
-  std::unique_ptr<char> buffer_;
+  std::unique_ptr<char[]> buffer_;
   size_t buffer_size_;
 
   Status Read(uint64_t offset, size_t size, Slice* result);