Remove special-case for twisted logger (matrix-org#12589)

This was originally added when we first added a `MemoryHandler` to the default
log config back in matrix-org#8040, to ensure
that we didn't explode with an infinite loop if there was an error formatting
the logs.

Since then, we made additional improvements to logging which make this
workaround redundant. In particular:

 * we no longer attempt to log un-UTF8-decodable byte sequences, which were the
   most likely cause of an error in the first place.

 * matrix-org#8268 ensures that in the unlikely
   case that there *is* an error, it won't cause an infinite loop.

changelog.d/12589.misc

@@ -0,0 +1 @@
+Remove special-case for `twisted` logger from default log config.

docs/sample_log_config.yaml

@@ -62,13 +62,6 @@ loggers:
         # information such as access tokens.
         level: INFO
 
-    twisted:
-        # We send the twisted logging directly to the file handler,
-        # to work around https://github.com/matrix-org/synapse/issues/3471
-        # when using "buffer" logger. Use "console" to log to stderr instead.
-        handlers: [file]
-        propagate: false
-
 root:
     level: INFO
 

synapse/config/logger.py

@@ -110,13 +110,6 @@
         # information such as access tokens.
         level: INFO
 
-    twisted:
-        # We send the twisted logging directly to the file handler,
-        # to work around https://github.com/matrix-org/synapse/issues/3471
-        # when using "buffer" logger. Use "console" to log to stderr instead.
-        handlers: [file]
-        propagate: false
-
 root:
     level: INFO