remove redundant import (clippy::single_component_path_imports)

remove redundant format!() call (clippy::useless_format)
don't use ok() before calling expect() (clippy::ok_expect)

src/librustdoc/passes/calculate_doc_coverage.rs

@@ -8,7 +8,6 @@ use rustc_ast::attr;
 use rustc_span::symbol::sym;
 use rustc_span::FileName;
 use serde::Serialize;
-use serde_json;
 
 use std::collections::BTreeMap;
 use std::ops;