Remove rust_2018_idioms for more modern Code

This will allow less unnecessary lifetimes in function signatures (instead of enforcing all)

Author: Byron

crates/but-rebase/src/lib.rs

@@ -1,7 +1,7 @@
 //! An API for an interactive rebases, suitable for interactive, UI driven, and programmatic use.
 //!
 //! It will only affect the commit-graph, and never the alter the worktree in any way.
-#![deny(rust_2018_idioms, missing_docs)]
+#![deny(missing_docs)]
 
 use crate::commit::DateMode;
 use anyhow::{Context, Ok, Result, anyhow, bail};

crates/but-testsupport/src/lib.rs

@@ -1,5 +1,5 @@
 //! Utilities for testing.
-#![deny(rust_2018_idioms, missing_docs)]
+#![deny(missing_docs)]
 
 use gix::Repository;
 use gix::bstr::{BStr, ByteSlice};