[S32/Temporal] retire TimeUnit enum and .delta
[S32/Temporal] retire TimeUnit enum and .delta

Use strings in .truncate-to instead.

.delta now becomes .later and .earlier, and they expect string keys as named
arguments.

tokuhirom/specs,perl6/specs,prammer/specs,perl6/specs,prammer/specs,tokuhirom/specs,prammer/specs,tokuhirom/specs