Make NN canonical->HIDL adapter execute* methods synchronous

This change alters the asynchronous execute* methods to be handled
synchronously (from the same thread) for three reasons:
1) To remove the need to use IPreparedModel::getUnderlyingResource
2) To simplify the code
3) To make the code more performant

Bug: N/A
Test: mma
Test: presubmit
Change-Id: I2c37deb03d1b1c34b0173bd741e55fce4de757f7