Reverted some of the nsc xpath API changes. In the revert, xpath_first() and xpath_vec() retain their old syntax with nsc==NULL.

The reason is to be conservative with the API. However, less used functions, such as xpath_vec_bool(), xpath_vec_ctx() and xpath_vec_flag()  are changed with a new `nsc`parameter, which should be set to NULL in most cases.

include/clixon_custom.h

@@ -48,9 +48,3 @@
  */
 #define USE_NETCONF_NS_AS_DEFAULT
 
-/* Make namespace check on RESTCONF PUT and POST -d data
- * Should be defined according to standard
- * Undefine it if you want allow no namespace (pick first name it finds in list
- * of loaded modules).
- */
-#define RESTCONF_NS_DATA_CHECK