Docs shouldn't refer to END

[tlimoncelli]

Describe the bug

Now that v4.15.0 shipped, we should remove END from the examples.

OLD:

D("example.com", REG_NONE, DnsProvider(DSP_POWERDNS),
    A("test", "1.2.3.4"),
END);

NEW:

D("example.com", REG_NONE, DnsProvider(DSP_POWERDNS),
    A("test", "1.2.3.4"),
);

END still works, but it isn't needed.