Fix SurfaceTexture listener performance

Attaching & detaching threads from JavaVM isn't cheap. There's
no reason to do a detach anyway, so just don't. This avoids
subsequent callbacks needing to re-attach.

This aligns SurfaceTexture to the common pattern elsewhere
in the platform for attaching as a daemon if it's not a java
thread.

Fixes: 26842782
Test: make
Change-Id: I9bebe288dc8896c1f2c47cc1b02409526926cef7