Remove docs for converting a legacy structured logging config. (#12392)

And update the upgrade notes to point at old versions of the documentation.

changelog.d/12392.doc

@@ -0,0 +1 @@
+Remove documentation for converting a legacy structured logging configuration to the new format.

docs/structured_logging.md

@@ -78,82 +78,3 @@ loggers:
 The above logging config will set Synapse as 'INFO' logging level by default,
 with the SQL layer at 'WARNING', and will log JSON formatted messages to a
 remote endpoint at 10.1.2.3:9999.
-
-## Upgrading from legacy structured logging configuration
-
-Versions of Synapse prior to v1.54.0 automatically converted the legacy
-structured logging configuration, which was deprecated in v1.23.0, to the standard
-library logging configuration.
-
-The following reference can be used to update your configuration. Based on the
-drain `type`, we can pick a new handler:
-
-1. For a type of `console`, `console_json`, or `console_json_terse`: a handler
-   with a class of `logging.StreamHandler` and a `stream` of `ext://sys.stdout`
-   or `ext://sys.stderr` should be used.
-2. For a type of `file` or `file_json`: a handler of `logging.FileHandler` with
-   a location of the file path should be used.
-3. For a type of `network_json_terse`: a handler of `synapse.logging.RemoteHandler`
-   with the host and port should be used.
-
-Then based on the drain `type` we can pick a new formatter:
-
-1. For a type of `console` or `file` no formatter is necessary.
-2. For a type of `console_json` or `file_json`: a formatter of
-   `synapse.logging.JsonFormatter` should be used.
-3. For a type of `console_json_terse` or `network_json_terse`: a formatter of
-   `synapse.logging.TerseJsonFormatter` should be used.
-
-For each new handler and formatter they should be added to the logging configuration
-and then assigned to either a logger or the root logger.
-
-An example legacy configuration:
-
-```yaml
-structured: true
-
-loggers:
-    synapse:
-        level: INFO
-    synapse.storage.SQL:
-        level: WARNING
-
-drains:
-    console:
-        type: console
-        location: stdout
-    file:
-        type: file_json
-        location: homeserver.log
-```
-
-Would be converted into a new configuration:
-
-```yaml
-version: 1
-
-formatters:
-    json:
-        class: synapse.logging.JsonFormatter
-
-handlers:
-    console:
-        class: logging.StreamHandler
-        stream: ext://sys.stdout
-    file:
-        class: logging.FileHandler
-        formatter: json
-        filename: homeserver.log
-
-loggers:
-    synapse:
-        level: INFO
-        handlers: [console, file]
-    synapse.storage.SQL:
-        level: WARNING
-```
-
-The new logging configuration is a bit more verbose, but significantly more
-flexible. It allows for configuration that were not previously possible, such as
-sending plain logs over the network, or using different handlers for different
-modules.

docs/upgrade.md

@@ -160,7 +160,7 @@ please upgrade Mjolnir to version 1.3.2 or later before upgrading Synapse.
 This release removes support for the `structured: true` logging configuration
 which was deprecated in Synapse v1.23.0. If your logging configuration contains
 `structured: true` then it should be modified based on the
-[structured logging documentation](structured_logging.md).
+[structured logging documentation](https://matrix-org.github.io/synapse/v1.56/structured_logging.html#upgrading-from-legacy-structured-logging-configuration).
 
 # Upgrading to v1.53.0
 
@@ -777,7 +777,7 @@ lock down external access to the Admin API endpoints.
 This release deprecates use of the `structured: true` logging
 configuration for structured logging. If your logging configuration
 contains `structured: true` then it should be modified based on the
-[structured logging documentation](structured_logging.md).
+[structured logging documentation](https://matrix-org.github.io/synapse/v1.56/structured_logging.html#upgrading-from-legacy-structured-logging-configuration).
 
 The `structured` and `drains` logging options are now deprecated and
 should be replaced by standard logging configuration of `handlers` and