Remove allocation tracking code from InfluxDB sampler for performance

On GitLab.com, InfluxSampler#sample_objects appears to take 1.2 s or so to
iterate through 1059 objects. This had led to delays of a couple hundred
milliseconds in processing in the main thread. Remove this code since it's not
really being used.

Closes gitlab-com/infrastructure#3250

changelogs/unreleased/sh-remove-allocation-tracking-influxdb.yml

+---
+title: Remove allocation tracking code from InfluxDB sampler for performance
+merge_request:
+author:
+type: performance

lib/gitlab/metrics/samplers/influx_sampler.rb

@@ -27,7 +27,6 @@ module Gitlab
         def sample
           sample_memory_usage
           sample_file_descriptors
-          sample_objects
           sample_gc
 
           flush
@@ -48,29 +47,6 @@ module Gitlab
           add_metric('file_descriptors', value: System.file_descriptor_count)
         end
 
-        if Metrics.mri?
-          def sample_objects
-            sample = Allocations.to_hash
-            counts = sample.each_with_object({}) do |(klass, count), hash|
-              name = klass.name
-
-              next unless name
-
-              hash[name] = count
-            end
-
-            # Symbols aren't allocated so we'll need to add those manually.
-            counts['Symbol'] = Symbol.all_symbols.length
-
-            counts.each do |name, count|
-              add_metric('object_counts', { count: count }, type: name)
-            end
-          end
-        else
-          def sample_objects
-          end
-        end
-
         def sample_gc
           time = GC::Profiler.total_time * 1000.0
           stats = GC.stat.merge(total_time: time)

spec/lib/gitlab/metrics/samplers/influx_sampler_spec.rb

@@ -21,7 +21,6 @@ describe Gitlab::Metrics::Samplers::InfluxSampler do
     it 'samples various statistics' do
       expect(sampler).to receive(:sample_memory_usage)
       expect(sampler).to receive(:sample_file_descriptors)
-      expect(sampler).to receive(:sample_objects)
       expect(sampler).to receive(:sample_gc)
       expect(sampler).to receive(:flush)
 
@@ -72,28 +71,6 @@ describe Gitlab::Metrics::Samplers::InfluxSampler do
     end
   end
 
-  if Gitlab::Metrics.mri?
-    describe '#sample_objects' do
-      it 'adds a metric containing the amount of allocated objects' do
-        expect(sampler).to receive(:add_metric)
-          .with(/object_counts/, an_instance_of(Hash), an_instance_of(Hash))
-          .at_least(:once)
-          .and_call_original
-
-        sampler.sample_objects
-      end
-
-      it 'ignores classes without a name' do
-        expect(Allocations).to receive(:to_hash).and_return({ Class.new => 4 })
-
-        expect(sampler).not_to receive(:add_metric)
-          .with('object_counts', an_instance_of(Hash), type: nil)
-
-        sampler.sample_objects
-      end
-    end
-  end
-
   describe '#sample_gc' do
     it 'adds a metric containing garbage collection statistics' do
       expect(GC::Profiler).to receive(:total_time).and_return(0.24)