Summary: When `use_direct_reads` and `use_direct_writes` are `false`, `logical_sector_size_` inside various `*File` implementations are not actually used, so `GetLogicalBlockSize` does not necessarily need to be called for `logical_sector_size_`, just set a default page size. This is a follow up PR for https://github.com/facebook/rocksdb/pull/6457. Pull Request resolved: https://github.com/facebook/rocksdb/pull/6522 Test Plan: make check Reviewed By: siying Differential Revision: D20408885 Pulled By: cheng-chang fbshipit-source-id: f2d3808f41265237e7fa2c0be9f084f8fa97fe3d