NNAPI Burst object cleanup

This CL addresses some follow up comments from ag/6154003 and
ag/6575732.

Bug: 119570067
Test: mma
Test: atest NeuralNetworksTest_static
Change-Id: I1a2bd4c9d97296f50d6ef9bb86515ea8e9a54515
Merged-In: I1a2bd4c9d97296f50d6ef9bb86515ea8e9a54515
(cherry picked from commit 39837fc8f4a1bfd4212490a393f3b4666f315e55)
12 files changed