gluon-web-model: remove unused field error message code

Validation errors are mostly handled in the frontend (by displaying
invalid fields with a red background). There was some code left in the
backend for handling different kinds of errors, and returning custom
error messages from validate(), but the resulting value was not used
anywhere.

package/gluon-web-model/luasrc/usr/lib/lua/gluon/web/model/classes.lua

@@ -186,6 +186,7 @@ function AbstractValue:__init__(...)
 
 	self.template  = "model/valuewrapper"
 
+	self.error = false
 	self.state = M.FORM_NODATA
 end
 
@@ -205,14 +206,9 @@ function AbstractValue:cfgvalue()
 	end
 end
 
-function AbstractValue:add_error(type, msg)
-	self.error = msg or type
-	self.state = M.FORM_INVALID
-end
-
 function AbstractValue:reset()
-	self.error = nil
 	self.data = nil
+	self.error = false
 	self.state = M.FORM_NODATA
 
 end
@@ -220,13 +216,9 @@ end
 function AbstractValue:parse(http)
 	self.data = self:formvalue(http)
 
-	local ok, err = self:validate()
-	if not ok then
-		if type(self.data) ~= "string" or #self.data > 0 then
-			self:add_error("invalid", err)
-		else
-			self:add_error("missing", err)
-		end
+	if not self:validate() then
+		self.error = true
+		self.state = M.FORM_INVALID
 		return
 	end