Super small improvement: Remove unnecessary mut (#3736)

## Issue Addressed

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Removed some unnecessary `mut`. 🙂 

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lcli/src/block_root.rs

@@ -37,7 +37,7 @@ use types::{EthSpec, FullPayload, SignedBeaconBlock};
 
 const HTTP_TIMEOUT: Duration = Duration::from_secs(5);
 
-pub fn run<T: EthSpec>(mut env: Environment<T>, matches: &ArgMatches) -> Result<(), String> {
+pub fn run<T: EthSpec>(env: Environment<T>, matches: &ArgMatches) -> Result<(), String> {
     let spec = &T::default_spec();
     let executor = env.core_context().executor;
 

lcli/src/eth1_genesis.rs

@@ -13,7 +13,7 @@ use types::EthSpec;
 pub const ETH1_GENESIS_UPDATE_INTERVAL: Duration = Duration::from_millis(7_000);
 
 pub fn run<T: EthSpec>(
-    mut env: Environment<T>,
+    env: Environment<T>,
     testnet_dir: PathBuf,
     matches: &ArgMatches<'_>,
 ) -> Result<(), String> {

lcli/src/skip_slots.rs

@@ -59,7 +59,7 @@ use types::{BeaconState, CloneConfig, EthSpec, Hash256};
 
 const HTTP_TIMEOUT: Duration = Duration::from_secs(10);
 
-pub fn run<T: EthSpec>(mut env: Environment<T>, matches: &ArgMatches) -> Result<(), String> {
+pub fn run<T: EthSpec>(env: Environment<T>, matches: &ArgMatches) -> Result<(), String> {
     let spec = &T::default_spec();
     let executor = env.core_context().executor;
 

lcli/src/transition_blocks.rs

@@ -94,7 +94,7 @@ struct Config {
     exclude_post_block_thc: bool,
 }
 
-pub fn run<T: EthSpec>(mut env: Environment<T>, matches: &ArgMatches) -> Result<(), String> {
+pub fn run<T: EthSpec>(env: Environment<T>, matches: &ArgMatches) -> Result<(), String> {
     let spec = &T::default_spec();
     let executor = env.core_context().executor;