Various cleanups

[samueltardieu]

Those various cleanups help ensure a build without warnings:

• Remove redundant imports
• Remove unused trait
• Do not use deprecated "cargo-clippy" feature check
• Replace objects instead of recreating them
• Define generic parameter bound in one place only
• Use Unix end-of-line convention for Rust source files
• Add missing documentation comment

This makes it easier to check that proposed pull requests do not introduce new warnings themselves.