Remove obsolete dist rules

The API files are disted to the apistubs/ subdir now, and all
known users have been updated to use that path.

Bug: 152479829
Test: No
Change-Id: I224fd5af8ba740c6ad94bbbdb20f5d53509e51f6
Merged-In: I224fd5af8ba740c6ad94bbbdb20f5d53509e51f6