Remove the module-lib-api target

This target existed just to track the "full" module lib API surface,
until the individual pieces had the same standards. However, now:
- the full current.txt file is available as a build target
- all the individual .txt files are API reviewed, checked against
last api, linted, and changes result on API council bug updates

The .txt files will be removed in a separate CL.

Bug: 171029603
Test: m checkapi
Change-Id: Ib8ec547871045f77fb73aa82f192b5a7767d0c33