clippy complains of redundant deref

[jayvdb]

warning: call to `.deref()` on a reference in this situation does nothing
   --> /home/jayvdb/rust/butane/butane_core/src/db/sqlite.rs:490:52
    |
490 |             return Err(Error::IncompatibleCustomT(v.deref().clone(), BACKEND_NAME))
    |                                                    ^^^^^^^^ help: remove this redundant call
    |
    = note: the type `SqlTypeCustom` does not implement `Deref`, so calling `deref` on `&SqlTypeCustom` copies the reference, which does not do anything and can be removed
    = note: `#[warn(noop_method_call)]` on by default

Not sure if we might want to implement Deref. Probably not.