DRTVWR-418: Fix API for LLTracker::stopTracking().

The signature for LLTracker::stopTracking() was silly: it accepted a void* for
the sole purpose of testing whether it was NULL. In other words, the parameter
was really a bool in void* clothing. Most callers passed NULL.

What got ugly was when you wanted to pass 'true', or a variable bool value.
Such values had to be cast to void*. In 64-bit land, the compiler correctly
flags that as extremely dubious practice.

But it's entirely unnecessary. Since stopTracking() wants a bool, change its
parameter to bool. Everybody wins.

(While at it, change a few related method params from BOOL to builtin bool.)