Remove the userinfo
This function removes the userinfo if present, without removing any authority.
assert( url( "http://user@example.com" ).remove_userinfo().has_userinfo() == false );
this->has_userinfo() == false && this->encoded_userinfo().empty == true
userinfo = [ [ user ] [ ':' password ] ]
user = *( unreserved / pct-encoded / sub-delims )
password = *( unreserved / pct-encoded / sub-delims / ":" )