Clean up linting warnings about unused imports.

warning: unused import: `std::result`
     --> database/src/types.rs:3:5
      |
    3 | use std::result;
      |     ^^^^^^^^^^^
      |
      = note: `#[warn(unused_imports)]` on by default

database/src/types.rs

@@ -1,6 +1,5 @@
 use std::convert::TryFrom;
 use std::fmt;
-use std::result;
 use std::str::FromStr;
 
 use anyhow::{Error, anyhow};