Enable clippy::redundant_guards (#8770)

This PR enables the
[`clippy::redundant_guards`](https://rust-lang.github.io/rust-clippy/master/index.html#/redundant_guards)
rule and fixes the outstanding violations.

Release Notes:

- N/A

tooling/xtask/src/main.rs

@@ -103,7 +103,6 @@ fn run_clippy(args: ClippyArgs) -> Result<()> {
         "clippy::non_canonical_clone_impl",
         "clippy::non_canonical_partial_ord_impl",
         "clippy::redundant_closure_call",
-        "clippy::redundant_guards",
         "clippy::reversed_empty_ranges",
         "clippy::single_range_in_vec_init",
         "clippy::suspicious_to_owned",