database: Remove #:reset-timestamps? from 'register-items'.

database: Remove #:reset-timestamps? from 'register-items'.

The assumption now is that the caller took care of resetting timestamps
and permissions.

* guix/store/database.scm (register-items): Remove #:reset-timestamps?
parameter and the call to 'reset-timestamps'.
(register-path): Adjust accordingly and add call to 'reset-timestamps'.
* gnu/build/image.scm (register-closure): Remove #:reset-timestamps?
parameter to 'register-items'.
* gnu/build/vm.scm (register-closure): Likewise.
* guix/nar.scm (finalize-store-file): Adjust accordingly.
* guix/scripts/pack.scm (store-database)[build]: Likewise.