warnings in mi-json.c

[Bruno Haible]

When compiling mi-json.c with CPPFLAGS=-Wall, I see a couple of warnings:

../../../testsuite/poke.mi-json/mi-json.c: In function ‘test_json_pk_sct’:
../../../testsuite/poke.mi-json/mi-json.c:250:7: warning: unused variable 
‘signed_p’ [-Wunused-variable]
   int signed_p;
       ^
../../../testsuite/poke.mi-json/mi-json.c: In function ‘test_json_file’:
../../../testsuite/poke.mi-json/mi-json.c:560:10: warning: unused variable 
‘len’ [-Wunused-variable]
   size_t len = 0;
          ^
../../../testsuite/poke.mi-json/mi-json.c:559:11: warning: unused variable 
‘nread’ [-Wunused-variable]
   ssize_t nread;
           ^
../../../testsuite/poke.mi-json/mi-json.c:557:24: warning: unused variable 
‘line’ [-Wunused-variable]
   char *poke_datadir, *line = NULL;
                        ^
../../../testsuite/poke.mi-json/mi-json.c:557:9: warning: unused variable 
‘poke_datadir’ [-Wunused-variable]
   char *poke_datadir, *line = NULL;
         ^

These are harmless. But it would be nice to clean them up nevertheless.

Bruno