Convert disting of api txt from mk to bp

droidstubs dist now dists the api file, so convert these manual
mk rules into bp dist instead.

Bug: 149293194
Test: m dist sdk && find out/dist/apistubs -name /android\.txt
Change-Id: I96052b427dc01a6d24b040ad0006129d4d1e48fb
Merged-In: I96052b427dc01a6d24b040ad0006129d4d1e48fb