Squelch Snowplow tracker log messages

These log messages often pollute structured log streams and do not
provide useful information. We tweak the log level to FATAL to suppress
all output.

https://github.com/snowplow/snowplow-ruby-tracker/pull/109
would make it possible to configure this logger directly.

Closes https://gitlab.com/gitlab-org/gitlab/issues/204755

changelogs/unreleased/sh-squelch-snowplow-tracker-messages.yml

+---
+title: Squelch Snowplow tracker log messages
+merge_request: 24809
+author:
+type: fixed

config/initializers/snowplow_tracker.rb

@@ -3,21 +3,12 @@
 # Gitlab.com uses Snowplow for identifying users and events.
 # https://gitlab.com/gitlab-org/gitlab/issues/6329
 #
-# SnowplowTracker write log into STDERR
+# SnowplowTracker writes logs to STDERR:
 # https://github.com/snowplow/snowplow-ruby-tracker/blob/39fcfa2be793f2e25e73087a9700abc93f43b5e8/lib/snowplow-tracker/emitters.rb#L23
-#     `LOGGER = Logger.new(STDERR)`
-#
-# In puma.rb, if `stdout_redirect` specify stderr, Puma will overwrite STDERR in:
-# https://github.com/puma/puma/blob/b41205f5cacbc2ad0060472bdce68ba636f42175/lib/puma/runner.rb#L134
-#    `STDERR.reopen stderr, (append ? "a" : "w")`
-# As a result, SnowplowTracker will log into Puma stderr, when Puma enabled.
-#
-# By default, SnowplowTracker uses default log formatter.
-# When enable Puma, SnowplowTracker log is expected to be JSON format, as part of puma_stderr.log.
-# Hence overwrite ::SnowplowTracker::LOGGER.formatter to JSON formatter
-
-if defined?(::Puma) && defined?(::SnowplowTracker::LOGGER)
-  ::SnowplowTracker::LOGGER.formatter = proc do |severity, datetime, progname, msg|
-    { severity: severity, timestamp: datetime.utc.iso8601(3), pid: $$, progname: progname, message: msg }.to_json << "\n"
-  end
+if defined?(::SnowplowTracker::LOGGER)
+  # This squelches the output of the logger since it doesn't really
+  # provide useful information.
+  # https://github.com/snowplow/snowplow-ruby-tracker/pull/109
+  # would make it possible to configure this logger directly.
+  ::SnowplowTracker::LOGGER.level = Logger::FATAL
 end