net: dns: Remove dns_client API and sample application

DNS resolving is better done with DNS resolve API so remove
the DNS client API which is quite hard to use.

Change-Id: Ide4973a5be674414ea6e04a35c938195cce40b6a
Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>
diff --git a/doc/zephyr.doxyfile b/doc/zephyr.doxyfile
index a2579b9..38912f9 100644
--- a/doc/zephyr.doxyfile
+++ b/doc/zephyr.doxyfile
@@ -109,7 +109,7 @@
                         ../lib/libc/minimal/include/ \
                         ../ext/lib/crypto/tinycrypt/include/ \
                         ../include/net/zoap.h \
-                        ../include/net/dns_client.h \
+                        ../include/net/dns_resolve.h \
                         ../tests/ztest/include/
 INPUT_ENCODING         = UTF-8
 FILE_PATTERNS          = "*.c" "*.h" "*.S"