Remove thread shutdown logic.

This logic wasn't right, and the kernel will clean
it up anyway. Since loading and unloading this library
isn't supported, I'm removing this race-prone section
of code until someone has a reason to and decides to
support this usecase.

Bug: 77934844
Test: (walleye) device boots/shutdowns w/o fatal errors
Change-Id: I2f7b8ed3c969c1e62879291424dfc6be20225dee