Clarify NNAPI control flow shape constraints RESTRICT AUTOMERGE

This change also removes some non-NN hashes in current.txt that were
unintentionally introduced in https://r.android.com/1178665.

Bug: 156918813
Bug: 158557728
Test: m
Change-Id: I4c2b83e11b27b791b3aa624be68474011b92a269
Merged-In: I4c2b83e11b27b791b3aa624be68474011b92a269
(cherry picked from commit 709842ab)