newrelic: fix crash during bootup caused by Rails.logger.

Using `Rails.logger` here causes server boot to fail with a `Undefined
method 'tagged'` error, possibly because `Rails.logger` isn't ready yet
during early initialization.

Gemfile.lock

@@ -295,7 +295,7 @@ GEM
     net-sftp (3.0.0)
       net-ssh (>= 5.0.0, < 7.0.0)
     net-ssh (6.1.0)
-    newrelic_rpm (7.1.0)
+    newrelic_rpm (7.2.0)
     nio4r (2.5.7)
     nokogiri (1.11.7)
       mini_portile2 (~> 2.5.0)

config/initializers/00_newrelic.rb

@@ -7,7 +7,7 @@ if Danbooru.config.new_relic_license_key.present?
     app_name: Danbooru.config.canonical_app_name,
     license_key: Danbooru.config.new_relic_license_key,
     log_level: Danbooru.config.debug_mode ? "debug" : "error",
-    log: Rails.logger,
+    #log: Rails.logger,
     "rake.tasks": ["maintenance:.*"],
     config: Rails.application.config,
   )