refactor: make it obvious that we always pass 0 to start-time-cpu-us

Instead of setting the variable to 0 unconditionally right before it is
used, just inline this zero into the only use-site.

Signed-off-by: Patrick Roy <roypat@amazon.co.uk>

src/jailer/src/env.rs

@@ -476,7 +476,7 @@ impl Env {
         Command::new(chroot_exec_file)
             .args(["--id", &self.id])
             .args(["--start-time-us", &self.start_time_us.to_string()])
-            .args(["--start-time-cpu-us", &self.start_time_cpu_us.to_string()])
+            .args(["--start-time-cpu-us", "0"])
             .args(["--parent-cpu-time-us", &self.jailer_cpu_time_us.to_string()])
             .stdin(Stdio::inherit())
             .stdout(Stdio::inherit())
@@ -698,8 +698,6 @@ impl Env {
         // Compute jailer's total CPU time up to the current time.
         self.jailer_cpu_time_us += get_time_us(ClockType::ProcessCpu);
         self.jailer_cpu_time_us -= self.start_time_cpu_us;
-        // Reset process start time.
-        self.start_time_cpu_us = 0;
 
         // If specified, exec the provided binary into a new PID namespace.
         if self.new_pid_ns {