Remove obsolete FIXME

brson said it's obsolete and I trust him.

Closes #2695

Author: catamorphism

src/rt/rust_sched_loop.cpp

@@ -134,8 +134,6 @@ rust_task *
 rust_sched_loop::schedule_task() {
     lock.must_have_lock();
     assert(this);
-    // FIXME: in the face of failing tasks, this is not always right. (#2695)
-    // assert(n_live_tasks() > 0);
     if (running_tasks.length() > 0) {
         size_t k = isaac_rand(&rctx);
         // Look around for a runnable task, starting at k.