Revert "Take DST into account when locating TimeZone from Numeric."

Reverting this as it's not the implementation that we would like it to be.
This is being used inside of ActiveSUpport::TimeZone[] and it's unaware
of the context in which to find the timezone period so the timezone found
changes depending on whether DST is in effect for the current period.
This means that `'2001-01-01'.in_time_zone(-9)` changes from winter/summer
even though it's the same date that we're trying to convert.

Since finding timezones by numeric offsets is a bit hit and miss we should
introduce a new API for finding them which supplies the date context in
which we want to search and we should probably also deprecate the finding
of timezones via the [] method, though this needs further discussion.

This reverts commit 2cc2fa3633.

activesupport/CHANGELOG.md

@@ -1,13 +1,3 @@
-*   Take DST into account when locating TimeZone from Numeric.
-
-    When given a specific offset, use the first result found where the
-    total current offset (including any periodic deviations such as DST)
-    from UTC is equal.
-
-    Fixes #15209.
-
-    *Yasyf Mohamedali*
-
 *   Added `#without` on `Enumerable` and `Array` to return a copy of an
     enumerable without the specified elements.
 

activesupport/lib/active_support/values/time_zone.rb

@@ -239,7 +239,7 @@ module ActiveSupport
           end
           when Numeric, ActiveSupport::Duration
             arg *= 3600 if arg.abs <= 13
-            all.find { |z| z.utc_total_offset == arg.to_i }
+            all.find { |z| z.utc_offset == arg.to_i }
           else
             raise ArgumentError, "invalid argument to TimeZone[]: #{arg.inspect}"
         end
@@ -285,12 +285,6 @@ module ActiveSupport
       end
     end
 
-    # Returns the offset of this time zone from UTC in seconds,
-    # taking DST into account.
-    def utc_total_offset
-      tzinfo.current_period.utc_total_offset if tzinfo
-    end
-
     # Returns the offset of this time zone as a formatted string, of the
     # format "+HH:MM".
     def formatted_offset(colon=true, alternate_utc_string = nil)

activesupport/test/core_ext/time_with_zone_test.rb

@@ -867,13 +867,6 @@ class TimeWithZoneMethodsForTimeAndDateTimeTest < ActiveSupport::TestCase
     end
   end
 
-  def test_in_time_zone_with_dst
-    travel_to(Time.utc(2014, 5, 20, 4, 59, 59))
-    time = Time.now.in_time_zone(-4)
-    assert_equal (-4*3600), time.time_zone.utc_total_offset
-    travel_back
-  end
-
   def test_in_time_zone_with_invalid_argument
     assert_raise(ArgumentError) {  @t.in_time_zone("No such timezone exists") }
     assert_raise(ArgumentError) { @dt.in_time_zone("No such timezone exists") }