Remove: do not check plural forms of translations.

There is no need for NewGRF to use the same plural forms for languages as OpenTTD.
Sometimes the plural forms change, and when that happens erroring on existing NML NewGRF is unreasonable.

nml/grfstrings.py

@@ -860,7 +860,6 @@ def isint(x, base=10):
     ("zh_TW", 0x0C, 1),
 ]
 LANG_NAMES = {lng[0]: lng[1] for lng in LANG_INFOS}
-LANG_PLURALS = {lng[1]: lng[2] for lng in LANG_INFOS}
 
 
 class Language:
@@ -1090,7 +1089,6 @@ def handle_grflangid(self, data, pos):
         if value < 0 or value >= 0x7F:
             raise generic.ScriptError("Invalid grflangid", pos)
         self.langid = value
-        self.check_expected_plural(None)
 
     def handle_plural(self, data, pos):
         """
@@ -1109,26 +1107,6 @@ def handle_plural(self, data, pos):
         if value < 0 or value > NUM_PLURAL_FORMS:
             raise generic.ScriptError("Invalid plural form", pos)
         self.plural = value
-        self.check_expected_plural(pos)
-
-    def check_expected_plural(self, pos):
-        """
-        Check whether the provided plural form of the language file
-        matches with the expected value for that language.
-
-        If not, raise an error.
-
-        @param pos: Position of the ##plural line, if position is available.
-        @type  pos: L{Position}
-        """
-        if self.plural is None or self.langid is None:
-            return
-
-        expected = LANG_PLURALS.get(self.langid)
-        if expected is not None and self.plural != expected:
-            msg = "Language with language id 0x{:02x} has plural form {:d} while the language uses plural form {:d}."
-            msg = msg.format(self.langid, self.plural, expected)
-            raise generic.ScriptError(msg, pos)
 
     def handle_gender(self, data, pos):
         """