Remove import_includes/export_includes

Now that ONE_SHOT_MAKEFILE no longer exists, we don't have to rely on
the filesystem to store this informtion.

This removes ~16.7k files from our build graph
(aosp-master/aosp_arm64-eng), though only about 600 of them were being
used in a normal build.

Test: treehugger
Change-Id: I3ac12f5ea7f11d25064109a0599bc5be1976fba5