Remove -logtodebugger option

(as discussed in #3377)
`-logtodebugger` is a strange, obscure, WIN32-only (mostly MSVC) thing. It went untested for a long time, so I'm pretty sure that noone is using it. 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.