[lldb] Remove logging from Platform::~Platform

Platform instances are stored in a function-local static list. However, the
logging code involves locking a function-local static mutex. This only works on
some implementations where the Log mutex is by accident destroyed *after* the
Platform list is destroyed.

This fixes randomly failing tests due to `recursive_mutex lock failed: Invalid
argument`.

Reviewed By: kastiglione

Differential Revision: https://reviews.llvm.org/D111816