Remove string_to_utc_time conversion function

This method was used in features that were removed (#268 and #271) and
the reason for converting ts values selected from the timeline query
is not explicitly documented in the commit history and appears to
be redundant (they are already timestamps)

lib/chrono_model/conversions.rb

@@ -6,19 +6,6 @@ module Conversions
 
     ISO_DATETIME = /\A(\d{4})-(\d\d)-(\d\d) (\d\d):(\d\d):(\d\d)(?:\.(\d+))?\z/
 
-    # rubocop:disable Style/PerlBackrefs
-    def string_to_utc_time(string)
-      return string if string.is_a?(Time)
-
-      return unless string =~ ISO_DATETIME
-
-      # .1 is .100000, not .000001
-      usec = $7.ljust(6, '0') unless $7.nil?
-
-      Time.utc $1.to_i, $2.to_i, $3.to_i, $4.to_i, $5.to_i, $6.to_i, usec.to_i
-    end
-    # rubocop:enable Style/PerlBackrefs
-
     def time_to_utc_string(time)
       time.to_fs(:db) << '.' << format('%06d', time.usec)
     end

lib/chrono_model/time_machine/timeline.rb

@@ -81,9 +81,7 @@ def timeline(record = nil, options = {})
         sql << " LIMIT #{options[:limit].to_i}" if options.key?(:limit)
 
         connection.on_schema(Adapter::HISTORY_SCHEMA) do
-          connection.select_values(sql, "#{name} periods").map! do |ts|
-            Conversions.string_to_utc_time ts
-          end
+          connection.select_values(sql, "#{name} periods")
         end
       end
 

spec/chrono_model/conversions_spec.rb

@@ -3,43 +3,6 @@
 require 'spec_helper'
 
 RSpec.describe ChronoModel::Conversions do
-  describe '.string_to_utc_time' do
-    subject(:string_to_utc_time) { described_class.string_to_utc_time(string) }
-
-    context 'with a valid UTC time string' do
-      let(:string) { '2017-02-06 09:46:31.129626' }
-
-      it { is_expected.to be_a(Time) }
-      it { expect(string_to_utc_time.year).to  eq 2017 }
-      it { expect(string_to_utc_time.month).to eq 2 }
-      it { expect(string_to_utc_time.day).to   eq 6 }
-      it { expect(string_to_utc_time.hour).to  eq 9 }
-      it { expect(string_to_utc_time.min).to   eq 46 }
-      it { expect(string_to_utc_time.sec).to   eq 31 }
-      it { expect(string_to_utc_time.usec).to  eq 129_626 } # Ref Issue #32
-    end
-
-    context 'with a valid UTC string without least significant zeros' do
-      let(:string) { '2017-02-06 09:46:31.129' }
-
-      it { is_expected.to be_a(Time) }
-      it { expect(string_to_utc_time.usec).to eq 129_000 } # Ref Issue #32
-    end
-
-    context 'with a valid UTC string without usec' do
-      let(:string) { '2017-02-06 09:46:31' }
-
-      it { is_expected.to be_a(Time) }
-      it { expect(string_to_utc_time.usec).to eq 0 }
-    end
-
-    context 'with an invalid UTC time string' do
-      let(:string) { 'foobar' }
-
-      it { is_expected.to be_nil }
-    end
-  end
-
   describe '.time_to_utc_string' do
     subject { described_class.time_to_utc_string(time) }