gnu: knot-resolver: Build with only knot:lib.

This saves 13.9 MiB (~7.5%) of total ‘guix size’.

* gnu/packages/dns.scm (knot-resolver)[inputs]: Replace knot with
knot:lib.

gnu/packages/dns.scm

@@ -986,7 +986,7 @@ synthesis, and on-the-fly re-configuration.")
     (inputs
      `(("fstrm" ,fstrm)
        ("gnutls" ,gnutls)
-       ("knot" ,knot)
+       ("knot:lib" ,knot "lib")
        ("libuv" ,libuv)
        ("lmdb" ,lmdb)
        ("luajit" ,luajit)