iot bootaction: provide default lib name

We want to provide a sane default for the bootaction library name so
that the developer isn't required to mess with read-only properties to
get this working.

Also small cleanup to remove duplicate and unused libs from Android.mk.

Bug: 67644323
Test: builds (master)
Test: properly loads default lib (nyc-iot-dev)
Test: logs and exits when lib doesn't exist (nyc-iot-dev)
Change-Id: I865a45f43b3594c99419e7e27c9798ee944d0db2