Remove -logtodebugger

`-logtodebugger` is a strange, obscure, WIN32-only (mostly MSVC) thing.
Let's clean up the options a bit get rid of it.

test_bitcoin was using fLogToDebugger as a way to prevent logging to
debug.log. For this, add a boolean (not exposed as option) fLogToDebugLog that
defaults to true and is disabled in the tests.