Remove method instrumentation for Banzai filters and reference parsers

For one README.md file, this instrumentation was adding several seconds and
significant RAM and CPU overhead since these filters often iterate through
all HTML nodes in tight loops.

Relates to #49409

changelogs/unreleased/sh-remove-banzai-instrumentation.yml

+---
+title: Remove method instrumentation for Banzai filters and reference parsers
+merge_request: 20770
+author:
+type: performance

config/initializers/8_metrics.rb

@@ -58,20 +58,6 @@ def instrument_classes(instrumentation)
     instrumentation.instrument_instance_methods(const)
   end
 
-  # Instruments all Banzai filters and reference parsers
-  {
-    Filter: Rails.root.join('lib', 'banzai', 'filter', '*.rb'),
-    ReferenceParser: Rails.root.join('lib', 'banzai', 'reference_parser', '*.rb')
-  }.each do |const_name, path|
-    Dir[path].each do |file|
-      klass = File.basename(file, File.extname(file)).camelize
-      const = Banzai.const_get(const_name).const_get(klass)
-
-      instrumentation.instrument_methods(const)
-      instrumentation.instrument_instance_methods(const)
-    end
-  end
-
   instrumentation.instrument_methods(Banzai::Renderer)
   instrumentation.instrument_methods(Banzai::Querying)