Call out the cache deleter related interface change in HISTORY.md (#6606)

Summary: Pull Request resolved: https://github.com/facebook/rocksdb/pull/6606

Reviewed By: riversand963

Differential Revision: D20708411

Pulled By: ltamasi

fbshipit-source-id: c15b4ded19a4b5c84e3e4240bdcec15460806c88

HISTORY.md

@@ -3,6 +3,7 @@
 ### Public API Change
 * Fix spelling so that API now has correctly spelled transaction state name `COMMITTED`, while the old misspelled `COMMITED` is still available as an alias.
 * Updated default format_version in BlockBasedTableOptions from 2 to 4. SST files generated with the new default can be read by RocksDB versions 5.16 and newer, and use more efficient encoding of keys in index blocks.
+* `Cache::Insert` now expects clients to pass in function objects implementing the `Cache::Deleter` interface as deleters instead of plain function pointers.
 
 ### Bug Fixes
 * Fix a bug where range tombstone blocks in ingested files were cached incorrectly during ingestion. If range tombstones were read from those incorrectly cached blocks, the keys they covered would be exposed.