BluetoothMidi: Remove unsafe code

In ag/16192242, several functions in Bluetooth relating to
characteristics were marked as unsafe and new ones were added.

This CL is meant to conform with these standards and potentially
remove a long standing bug.

Bug: 146385555
Test: Added Identity Reply/Request code to MIDIMatrix
and tested with Yamaha MD-BT01 for Android T->T, T->R, R->T
Change-Id: I07311296509d4d042fc92aec327f40993d2e6f54
1 file changed