[time.format] Remove mid-sentence 'subclause' introducer from external reference

Author: tkoeppe

source/time.tex

@@ -10797,7 +10797,7 @@
 the locale's alternative full year representation.
 \\ \rowsep
 \tcode{\%z} &
-The offset from UTC as specified in ISO 8601-1:2019, subclause 5.3.4.1.
+The offset from UTC as specified in ISO 8601-1:2019, 5.3.4.1.
 For example \tcode{-0430} refers to 4 hours 30 minutes behind UTC\@.
 If the offset is zero, \tcode{+0000} is used.
 The modified commands \tcode{\%Ez} and  \tcode{\%Oz}