Per discussion in D28616, having two ways two request logging (log
enable lldb XXX verbose && log enable -v lldb XXX) is confusing. This
removes the first option and standardizes all code to use the second
I've added a LLDB_LOGV macro as a shorthand for if(log &&
log->GetVerbose()) and switched most of the affected log statements to
use that (I've only left a couple of cases that were doing complex
computations in an if(log) block).