[S17] unspec $*TICK

It's problematic in that it assumes a single global
scheduler. It also seems to punish the many for a
feature only benefiting the few.

There are preferable ways to handle this, perhaps
something like
Supply.interval(:at(now.ceiling), :every(1))

S17-concurrency.pod

@@ -631,9 +631,6 @@ $*POSIX is a Supply in which POSIX signals received by the running
 process, will appear as C<POSIX::Signal> objects to taps.  On
 non-POSIX systems, a similar Supply will exist to handle system events.
 
-The $*TICK Supply generates an L<Instant> object at the top of every
-second for any taps.
-
 =head2 Threads
 
 VM-level threads, which typically correspond to OS-level threads, are exposed