Revert curl ratelimit

as mentioned in https://github.com/xbmc/xbmc/commit/241a4fc0babb108f652b993b2b40a20397433118#commitcomment-3190048 we are going to revert the non-generic ratelimit code recently added into curl. and if still need the feature, we need a better implement which not affect other codes using CurlFile.

@night199uk @jmarshallnz