Remove incorrect comment in ActiveRecord::Type::Value

Says it's only used for the schema, but they are in fact used for
other things. Integer verifies against the limit during casting,
and Decimal uses precision during casting. It may be true that
scale is only used for the schema.

activerecord/lib/active_record/type/value.rb

@@ -3,8 +3,7 @@ module Type
     class Value # :nodoc:
       attr_reader :precision, :scale, :limit
 
-      # Valid options are +precision+, +scale+, and +limit+. They are only
-      # used when dumping schema.
+      # Valid options are +precision+, +scale+, and +limit+.
       def initialize(options = {})
         options.assert_valid_keys(:precision, :scale, :limit)
         @precision = options[:precision]