Consolidate NNAPI OWNERS files

This change deletes all existing OWNERS files under
hardware/interfaces/neuralnetworks and creates a new OWNERS file with
the current NNAPI team members.

This change also updates the NNAPI project path in
hardware/interfaces/neuralnetworks/README.

Bug: 179510251
Test: N/A
Change-Id: Iaca69505c8449ae7d93be0db99205f5f56556e86