UTIL: Fix compilation of sss_utf8 with libunistring
    
    The internal header file "util/util.h" was removed from sss_utf8.h
    as part of commit de5fa34860886ad68fba5e739987e16c342e8f14.
    It was neccessary to ensure libipa_hbac can be build with C90
    compatible compiler.
    
    This header file includes many system header file and after
    this change caused missing declaration of the function free()
    
    src/util/sss_utf8.c: In function ‘sss_utf8_free’:
    src/util/sss_utf8.c:40:12: error: implicit declaration of function ‘free’
      [-Werror=implicit-function-declaration]
         return free(ptr);
                ^~~~
    src/util/sss_utf8.c:40:12: warning: incompatible implicit declaration
                                        of built-in function ‘free’
    src/util/sss_utf8.c:40:12: note: include ‘<stdlib.h>’ or provide
                                     a declaration of ‘free’
    cc1: some warnings being treated as errors
    
    Reviewed-by: Fabiano Fidêncio <fidencio@redhat.com>
    (cherry picked from commit c101cb130df0705a9227dadce22554307eee54db)