Summary:
The patch does some cleanup in and around the legacy `BlobLogReader` class:
* It renames the class to `BlobLogSequentialReader` to emphasize that it is for
sequentially iterating through blobs in a blob file, as opposed to doing random
point reads using `BlobIndex`es (which is `BlobFileReader`'s jurisdiction).
* It removes some dead code from the old BlobDB implementation that references
`BlobLogReader` (namely the method `BlobFile::OpenRandomAccessReader`).
* It cleans up some `#include`s and forward declarations.
* It fixes some incorrect/outdated comments related to the reader class.
* It adds a few assertions to the `Read` methods of the class.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/7517
Test Plan: `make check`
Reviewed By: riversand963
Differential Revision: D24172611
Pulled By: ltamasi
fbshipit-source-id: 43e2ae1eba5c3dd30c1070cb00f217edc45bd64f
1f84611e5d