Remove largely useless bit of test log to silence GCC 12

GCC 12 emits a warning because it thinks `buffer1` is used after having been
freed. The code is correct C because we're only using the value of
`(uintptr_t)buffer1`, not `buffer1`. However, we aren't using the value for
anything useful: it doesn't really matter if an alloc-free-alloc sequence
returns the same address twice. So don't print that bit of information, and
this way we don't need to save the old address.

Fixes #5974.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

ChangeLog.d/selftest-gcc12.txt

@@ -0,0 +1,2 @@
+Bugfix
+   * Silence a warning from GCC 12 in the selftest program. Fixes #5974.

programs/test/selftest.c

@@ -89,7 +89,6 @@ static int calloc_self_test( int verbose )
     void *empty2 = mbedtls_calloc( 0, 1 );
     void *buffer1 = mbedtls_calloc( 1, 1 );
     void *buffer2 = mbedtls_calloc( 1, 1 );
-    uintptr_t old_buffer1;
 
     if( empty1 == NULL && empty2 == NULL )
     {
@@ -131,7 +130,6 @@ static int calloc_self_test( int verbose )
             mbedtls_printf( "  CALLOC(1): passed\n" );
     }
 
-    old_buffer1 = (uintptr_t) buffer1;
     mbedtls_free( buffer1 );
     buffer1 = mbedtls_calloc( 1, 1 );
     if( buffer1 == NULL )
@@ -143,9 +141,7 @@ static int calloc_self_test( int verbose )
     else
     {
         if( verbose )
-            mbedtls_printf( "  CALLOC(1 again): passed (%s address)\n",
-                            (uintptr_t) old_buffer1 == (uintptr_t) buffer1 ?
-                            "same" : "different" );
+            mbedtls_printf( "  CALLOC(1 again): passed\n" );
     }
 
     if( verbose )