[pkg] Use new MockPaver Hooks.

This replaces usage of the `config_hook`, `config_status_hook`,
`firmware_hook`, and `read_hook` methods of MockPaver with equivalent
calls to the `insert_hook` method introduced in fxrev.dev/448895.

Change-Id: Id9d2651a230cb3b7ad2076ed9f616540700b6931
Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/450134
Reviewed-by: Ben Keller <galbanum@google.com>
Testability-Review: Ben Keller <galbanum@google.com>
Commit-Queue: Hunter Freyer <hjfreyer@google.com>