agent: Fix .enumerate errors during make check

Running `make check` in the `src/agent` directory gives:

```
error: you seem to use `.enumerate()` and immediately discard the index
   --> rustjail/src/mount.rs:572:27
    |
572 |     for (_index, line) in reader.lines().enumerate() {
    |                           ^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#unused_enumerate_index
    = note: `-D clippy::unused-enumerate-index` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(clippy::unused_enumerate_index)]`
help: remove the `.enumerate()` call
    |
572 |     for line in reader.lines() {
    |         ~~~~    ~~~~~~~~~~~~~~

    Checking tokio-native-tls v0.3.1
    Checking hyper-tls v0.5.0
    Checking reqwest v0.11.18
error: could not compile `rustjail` (lib) due to 1 previous error
warning: build failed, waiting for other jobs to finish...
make: *** [../../utils.mk:177: standard_rust_check] Error 101
```

Fixes: #9342

Signed-off-by: Christophe de Dinechin <dinechin@redhat.com>

src/agent/rustjail/src/mount.rs

@@ -569,7 +569,7 @@ pub fn parse_mount_table(mountinfo_path: &str) -> Result<Vec<Info>> {
     let reader = BufReader::new(file);
     let mut infos = Vec::new();
 
-    for (_index, line) in reader.lines().enumerate() {
+    for line in reader.lines() {
         let line = line?;
 
         //Example mountinfo format:

src/agent/src/mount.rs

@@ -180,7 +180,7 @@ pub fn get_mount_fs_type_from_file(mount_file: &str, mount_point: &str) -> Resul
     let re = Regex::new(format!("device .+ mounted on {} with fstype (.+)", mount_point).as_str())?;
 
     // Read the file line by line using the lines() iterator from std::io::BufRead.
-    for (_index, line) in content.lines().enumerate() {
+    for line in content.lines() {
         if let Some(capes) = re.captures(line) {
             if capes.len() > 1 {
                 return Ok(capes[1].to_string());
@@ -225,7 +225,7 @@ pub fn get_cgroup_mounts(
 
     // #subsys_name    hierarchy       num_cgroups     enabled
     // fields[0]       fields[1]       fields[2]       fields[3]
-    'outer: for (_, line) in reader.lines().enumerate() {
+    'outer: for line in reader.lines() {
         let line = line?;
 
         let fields: Vec<&str> = line.split('\t').collect();