Removed UUIDs from metrics transactions

While useful for finding out what methods/views belong to a transaction
this might result in too much data being stored in InfluxDB.

lib/gitlab/metrics/transaction.rb

@@ -4,7 +4,7 @@ module Gitlab
     class Transaction
       THREAD_KEY = :_gitlab_metrics_transaction
 
-      attr_reader :uuid, :tags
+      attr_reader :tags
 
       def self.current
         Thread.current[THREAD_KEY]
@@ -12,7 +12,6 @@ module Gitlab
 
       def initialize
         @metrics = []
-        @uuid    = SecureRandom.uuid
 
         @started_at  = nil
         @finished_at = nil
@@ -38,7 +37,6 @@ module Gitlab
       end
 
       def add_metric(series, values, tags = {})
-        tags   = tags.merge(transaction_id: @uuid)
         prefix = sidekiq? ? 'sidekiq_' : 'rails_'
 
         @metrics << Metric.new("#{prefix}#{series}", values, tags)

spec/lib/gitlab/metrics/transaction_spec.rb

@@ -30,9 +30,9 @@ describe Gitlab::Metrics::Transaction do
   end
 
   describe '#add_metric' do
-    it 'adds a metric tagged with the transaction UUID' do
+    it 'adds a metric to the transaction' do
       expect(Gitlab::Metrics::Metric).to receive(:new).
-        with('rails_foo', { number: 10 }, { transaction_id: transaction.uuid })
+        with('rails_foo', { number: 10 }, {})
 
       transaction.add_metric('foo', number: 10)
     end