Editorial: align SystemTimeZoneIdentifier to 262

This commit rebases one line of SystemTimeZoneIdentifier on
tc39/ecma262#3104.

spec/timezone.html

@@ -29,17 +29,11 @@ <h1>SystemTimeZoneIdentifier ( ): a String</h1>
     <emu-alg>
       1. If the implementation only supports the UTC time zone, return *"UTC"*.
       1. Let _systemTimeZoneString_ be the String representing the host environment's current time zone, either a primary time zone identifier or an offset time zone identifier.
-      1. If IsTimeZoneOffsetString(_systemTimeZoneString_) is *true*, return <del>_systemTimeZoneString_</del><ins>CanonicalizeTimeZoneOffsetString(_systemTimeZoneString_)</ins>.
+      1. <ins>If IsTimeZoneOffsetString(_systemTimeZoneString_) is *true*, return CanonicalizeTimeZoneOffsetString(_systemTimeZoneString_)</ins>.
       1. Return _systemTimeZoneString_.
     </emu-alg>
 
-    <emu-note>
-      <p>
-        To ensure the level of functionality that implementations commonly provide in the methods of the Date object, it is recommended that SystemTimeZoneIdentifier return an IANA time zone name corresponding to the host environment's time zone setting, if such a thing exists.
-        GetNamedTimeZoneEpochNanoseconds and GetNamedTimeZoneOffsetNanoseconds must reflect the local political rules for standard time and daylight saving time in that time zone, if such rules exist.
-      </p>
-      <p>For example, if the host environment is a browser on a system where the user has chosen US Eastern Time as their time zone, SystemTimeZoneIdentifier returns *"America/New_York"*.</p>
-    </emu-note>
+    <p>[...]</p>
   </emu-clause>
 
   <emu-clause id="sec-temporal-timezone-objects">