Editorial: Replace dead code by an assertion.

Author: Ms2ger

spec/timezone.html

@@ -503,7 +503,8 @@ <h1>ParseTimeZoneOffsetString ( _offsetString_ )</h1>
         1. If _offsetString_ does not satisfy the syntax of a |TimeZoneNumericUTCOffset| (see <emu-xref href="#sec-temporal-iso8601grammar"></emu-xref>), then
           1. Throw a *RangeError* exception.
         1. Let _sign_, _hours_, _minutes_, _seconds_, and _fraction_ be the parts of _offsetString_ produced respectively by the |TimeZoneUTCOffsetSign|, |TimeZoneUTCOffsetHour|, |TimeZoneUTCOffsetMinute|, |TimeZoneUTCOffsetSecond|, and |TimeZoneUTCOffsetFraction| productions, or *undefined* if not present.
-        1. If either _hours_ or _sign_ are *undefined*, throw a *RangeError* exception.
+        1. Assert: _sign_ is not *undefined*.
+        1. Assert: _hours_ is not *undefined*.
         1. If _sign_ is the code unit 0x002D (HYPHEN-MINUS) or 0x2212 (MINUS SIGN), then
           1. Set _sign_ to −1.
         1. Else,