ThreadPool: don't silently ignore non-std exceptions

Introduced in 8f6b347 without explanation.

Throwing anything that's not that is a programming mistake that we don't want
to ignore silently. A crash would be ok, because that means we/they can fix
the offending throw.

src/libutil/thread-pool.cc

@@ -119,7 +119,6 @@ void ThreadPool::doWork(bool mainThread)
                             // Similarly expected.
                         } catch (std::exception & e) {
                             ignoreExceptionExceptInterrupt();
-                        } catch (...) {
                         }
                     }
                 }