remove use of "HLL".

Author: coke

doc/Type/Thread.pod6

@@ -141,7 +141,7 @@ L<name|#method_name>.
 
 Returns a Bool indicating whether the current thread (if called as a class
 method) or the Thread object on which it is called, is the initial thread
-of the program seen from a HLL-language perspective.
+the program started on.
 
     say Thread.is-initial-thread;    # True if this is the initial thread
     say $*THREAD.is-initial-thread;  # True if $*THREAD is the initial thread