Update reference to lang.h whiche moved to l18nlangtag module

Followup to commit 876c619b

Change-Id: I087f0c976e3c3d47e920280e353b3e142d5e2bfd

i18npool/source/localedata/data/locale.dtd

@@ -159,7 +159,7 @@
      Note: The brackets and the leading $ character are mandatory, the
      hyphen-minus separates the currency symbol from the hexagesimal MS-LCID,
      letters contained in the LCID have to be in upper case, leading zeros are
-     to be omitted. LCIDs are defined in i18npool/inc/i18npool/lang.h
+     to be omitted. LCIDs are defined in i18nlangtag/inc/i18nlangtag/lang.h
 -->
 
 <!ELEMENT DateAcceptancePattern (#PCDATA)>