According to some internal communication, these two functions are place
holders for future enhancements. Because they use a variable number of
parameters, the implementation defined a reserved keyword for them in the
parser grammar.

Unfortunately, doing so creates a bug similar to Bug 21114 reported for the
function FORMAT.

In the 5.1 code base, due to improvements in the code implemented with bug
21114, having a reserved keyword for functions with a variable number of
arguments is not needed any more by the implementation.

As a result, this fix removes the place-holder implementation, and removes
the unnecessary reserved keywords. Should the functions UNIQUE_USERS and
GROUP_UNIQUE_USERS be finally implemented in a later release, the
implementation should sub class Create_native_func in sql/item_create.cc.
For example, see the class Create_func_concat.


BitKeeper/deleted/.del-item_uniq.cc:
  Rename: sql/item_uniq.cc -> BitKeeper/deleted/.del-item_uniq.cc
BitKeeper/deleted/.del-item_uniq.h:
  Rename: sql/item_uniq.h -> BitKeeper/deleted/.del-item_uniq.h
libmysqld/Makefile.am:
  Remove native functions UNIQUE_USERS() and GROUP_UNIQUE_USERS().
mysql-test/r/parser.result:
  Remove native functions UNIQUE_USERS() and GROUP_UNIQUE_USERS().
mysql-test/t/parser.test:
  Remove native functions UNIQUE_USERS() and GROUP_UNIQUE_USERS().
sql/Makefile.am:
  Remove native functions UNIQUE_USERS() and GROUP_UNIQUE_USERS().
sql/item.h:
  Remove native functions UNIQUE_USERS() and GROUP_UNIQUE_USERS().
sql/item_sum.h:
  Remove native functions UNIQUE_USERS() and GROUP_UNIQUE_USERS().
sql/lex.h:
  Remove native functions UNIQUE_USERS() and GROUP_UNIQUE_USERS().
sql/mysql_priv.h:
  Remove native functions UNIQUE_USERS() and GROUP_UNIQUE_USERS().
sql/sql_yacc.yy:
  Remove native functions UNIQUE_USERS() and GROUP_UNIQUE_USERS().