wallet: remove unused DatabaseOptions members

`use_shared_memory` and `max_log_mb` are never read or written; they
only ever hold their initializers. Their last readers, in
`GetBerkeleyEnv()` and the `BerkeleyDatabase` constructor, were removed
in 04a7a7a28c ("build, wallet, doc: Remove BDB"), along with the
`-privdb` and `-dblogsize` options that set them.

Co-authored-by: pablomartin4btc <pablomartin4btc@gmail.com>

src/wallet/db.h

@@ -175,8 +175,6 @@ struct DatabaseOptions {
     // Specialized options. Not every option is supported by every backend.
     bool verify = true;             //!< Check data integrity on load.
     bool use_unsafe_sync = false;   //!< Disable file sync for faster performance.
-    bool use_shared_memory = false; //!< Let other processes access the database.
-    int64_t max_log_mb = 100;       //!< Max log size to allow before consolidating.
 };
 
 enum class DatabaseStatus {