random_init_delay: remove the minimum of 10 seconds

Before this patch, the range from which the random delay is picked
is at minimum 10 seconds.

The disk usage eviction tests are apparently the first to wait for
a background loop to do its job.
With this patch, they only need to wait the 1s which they configure.

pageserver/src/tenant/tasks.rs

@@ -244,14 +244,12 @@ pub(crate) async fn random_init_delay(
 ) -> Result<(), Cancelled> {
     use rand::Rng;
 
+    if period == Duration::ZERO {
+        return Ok(());
+    }
+
     let d = {
         let mut rng = rand::thread_rng();
-
-        // gen_range asserts that the range cannot be empty, which it could be because period can
-        // be set to zero to disable gc or compaction, so lets set it to be at least 10s.
-        let period = std::cmp::max(period, Duration::from_secs(10));
-
-        // semi-ok default as the source of jitter
         rng.gen_range(Duration::ZERO..=period)
     };