Common: Remove async logging

It provided a large increase in complexity of the logging system while
having a negligible performance impact: the usage patterns of the ring
buffer meant that each log contended with the logging thread, causing
it to effectively act as a synchronous extra buffering.

Also removed some broken code related to filtering of subclasses which
was broken since it was introduced. (Which means no one ever used that
feature anyway, since, 8 months later, no one ever complained.)

src/common/logging/text_formatter.h

@@ -5,11 +5,9 @@
 #pragma once
 
 #include <cstddef>
-#include <memory>
 
 namespace Log {
 
-class Logger;
 struct Entry;
 
 /**
@@ -31,10 +29,4 @@ void PrintMessage(const Entry& entry);
 /// Prints the same message as `PrintMessage`, but colored acoording to the severity level.
 void PrintColoredMessage(const Entry& entry);
 
-/**
- * Logging loop that repeatedly reads messages from the provided logger and prints them to the
- * console. It is the baseline barebones log outputter.
- */
-void TextLoggingLoop(std::shared_ptr<Logger> logger);
-
 }