Remove DateTime#to_time override

Currently if the offset is not zero then to_time returns self which
can lead to errors where a developer assumes that the value is a
Time. To solve this we can use the native implementation of
DateTime#to_time in Ruby 1.9.3 as it handles offsets properly and
is faster than our override.

activesupport/lib/active_support/core_ext/date_time/conversions.rb

@@ -4,10 +4,6 @@
 require 'active_support/values/time_zone'
 
 class DateTime
-  # Ruby 1.9 has DateTime#to_time which internally relies on Time. We define our own #to_time which allows
-  # DateTimes outside the range of what can be created with Time.
-  remove_method :to_time
-
   # Convert to a formatted string. See Time::DATE_FORMATS for predefined formats.
   #
   # This method is aliased to <tt>to_s</tt>.
@@ -57,16 +53,6 @@ def readable_inspect
   alias_method :default_inspect, :inspect
   alias_method :inspect, :readable_inspect
 
-  # Attempts to convert self to a Ruby Time object; returns self if out of range of Ruby Time class.
-  # If self has an offset other than 0, self will just be returned unaltered, since there's no clean way to map it to a Time.
-  def to_time
-    if offset == 0
-      ::Time.utc_time(year, month, day, hour, min, sec, sec_fraction * 1000000)
-    else
-      self
-    end
-  end
-
   # Returns DateTime with local offset for given year if format is local else offset is zero
   #
   #   DateTime.civil_from_format :local, 2012