Resolve Rust 1.56 lints and warnings (#2728)

## Issue Addressed

When compiling with Rust 1.56.0 the compiler generates 3 instances of this warning:

```
warning: trailing semicolon in macro used in expression position
   --> common/eth2_network_config/src/lib.rs:181:24
    |
181 |                     })?;
    |                        ^
...
195 |         let deposit_contract_deploy_block = load_from_file!(DEPLOY_BLOCK_FILE);
    |                                             ---------------------------------- in this macro invocation
    |
    = note: `#[warn(semicolon_in_expressions_from_macros)]` on by default
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #79813 <https://github.com/rust-lang/rust/issues/79813>
    = note: this warning originates in the macro `load_from_file` (in Nightly builds, run with -Z macro-backtrace for more info)
```

This warning is completely harmless, but will be visible to users compiling Lighthouse v2.0.1 (or earlier) with Rust 1.56.0 (to be released October 21st). It is **completely safe** to ignore this warning, it's just a superficial change to Rust's syntax.

## Proposed Changes

This PR removes the semi-colon as recommended, and fixes the new Clippy lints from 1.56.0

common/eth2_network_config/src/lib.rs

@@ -178,7 +178,7 @@ impl Eth2NetworkConfig {
                     .and_then(|file| {
                         serde_yaml::from_reader(file)
                             .map_err(|e| format!("Unable to parse {}: {:?}", $file, e))
-                    })?;
+                    })?
             };
         }