Fix new clippy lints (#2036)

## Issue Addressed

NA

## Proposed Changes

Fixes new clippy lints in the whole project (mainly [manual_strip](https://rust-lang.github.io/rust-clippy/master/index.html#manual_strip) and [unnecessary_lazy_evaluations](https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_lazy_evaluations)). Furthermore, removes `to_string()` calls on literals when used with the `?`-operator.

crypto/eth2_wallet/src/wallet.rs

@@ -202,7 +202,7 @@ impl Wallet {
             .json
             .nextaccount
             .checked_add(1)
-            .ok_or_else(|| Error::PathExhausted)?;
+            .ok_or(Error::PathExhausted)?;
 
         Ok(keystores)
     }