async_hooks: don't set hook_fields[kTotals] to 0

This commit removes the setting of hook_field[kTotals] to szero in
AsyncHook's enable function.

As far as I can tell this would not be required if the setting of
this field is done with the assignment operator instead of using the
addition assignment operator.

PR-URL: https://github.com/nodejs/node/pull/19219


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>