Remove clippy deny attributes from test suite

These were superseded by the clippy invocation made in our CI workflow:

    run: cargo clippy --tests -- -Dclippy::all -Dclippy::pedantic

tests/compiletest.rs

@@ -1,5 +1,3 @@
-#![deny(clippy::all, clippy::pedantic)]
-
 #[rustversion::attr(not(nightly), ignore)]
 #[cfg_attr(miri, ignore)]
 #[test]

tests/test_display.rs

@@ -1,5 +1,3 @@
-#![deny(clippy::all, clippy::pedantic)]
-
 use std::fmt::Display;
 use thiserror::Error;
 

tests/test_error.rs

@@ -1,4 +1,3 @@
-#![deny(clippy::all, clippy::pedantic)]
 #![allow(dead_code)]
 
 use std::fmt::{self, Display};

tests/test_expr.rs

@@ -1,4 +1,3 @@
-#![deny(clippy::all, clippy::pedantic)]
 #![allow(clippy::iter_cloned_collect, clippy::option_if_let_else)]
 
 use std::fmt::Display;

tests/test_from.rs

@@ -1,5 +1,3 @@
-#![deny(clippy::all, clippy::pedantic)]
-
 use std::io;
 use thiserror::Error;
 

tests/test_generics.rs

@@ -1,4 +1,3 @@
-#![deny(clippy::all, clippy::pedantic)]
 #![allow(clippy::needless_late_init)]
 
 use std::fmt::{self, Debug, Display};

tests/test_option.rs

@@ -1,5 +1,4 @@
 #![cfg_attr(thiserror_nightly_testing, feature(backtrace))]
-#![deny(clippy::all, clippy::pedantic)]
 
 #[cfg(thiserror_nightly_testing)]
 pub mod structs {

tests/test_path.rs

@@ -1,5 +1,3 @@
-#![deny(clippy::all, clippy::pedantic)]
-
 use ref_cast::RefCast;
 use std::fmt::Display;
 use std::path::{Path, PathBuf};

tests/test_source.rs

@@ -1,5 +1,3 @@
-#![deny(clippy::all, clippy::pedantic)]
-
 use std::error::Error as StdError;
 use std::io;
 use thiserror::Error;

tests/test_transparent.rs

@@ -1,5 +1,3 @@
-#![deny(clippy::all, clippy::pedantic)]
-
 use anyhow::anyhow;
 use std::error::Error as _;
 use std::io;