Remove protocol 'file' for evseimageurltype

[ahzf]

The evseImageUrlType in https://github.com/e-clearing-net/OCHP/blob/master/OCHP.md#evseimageurltype-class has a regular expression for verification which allows the "file" protocol type beside http, https, ftp. As 'file' means "this computer" https://en.wikipedia.org/wiki/File_URI_scheme it is unlikely that it will make much sense in the OCHP protocol. Therefore I would suggest to remove it.