gfile: Do not return target-uri from g_file_peek_path()

Documentation says that g_file_peek_path() returns exactly the same what g_file_get_path(), but this is not true. Apart from that the code segfaults for some uris (e.g. for "trash:///"), it returns target-uri for trash and recent schemes. This is unexpected and can lead to various issues among others because the target-uri paths are not automatically translated back to GDaemonFile as it is done with gvfsd-fuse paths. g_file_get_path() returns NULL for trash and recent schemes, because fuse paths are not provided for those schemes. So g_file_peek_path() should return NULL as well. It is up to the concrete application to use target-uri when appropriate.

This change was made as a part of commit 4808a957, however, neither the commit message, neither the corresponding bug doesn't mention this crucial change and doesn't give any clear reasoning. So let's revert this.