Fix missing Handle release in TableCache::GetRangeTombstoneIterator (#8589)

Fix missing Handle release in TableCache::GetRangeTombstoneIterator (#8589)

Summary:
This appears to be little used code so not a major bug, but is
blocking https://github.com/facebook/rocksdb/issues/8544

Pull Request resolved: https://github.com/facebook/rocksdb/pull/8589

Test Plan:
Added regression test to the end of
DBRangeDelTest::TableEvictedDuringScan. Without this fix, ASAN reports
memory leak.

Reviewed By: ajkr

Differential Revision: D29943623

Pulled By: pdillinger

fbshipit-source-id: f7115fa6d4440aef83888ff609aa03d09216463b