allow named remote-servers list with key or tls

allow named remote-servers list with key or tls

The remote-servers clause enables the following pattern:

	remote-servers a { 1.2.3.4; ... };
	remote-servers b { a key foo; };

However, `check.c` was explicitly throwing an error if a `key` or `tls`
was provided after a named server-list. Remove this check, as this is a
valid use case.