Fix harmless compiler warnings.

FossilOrigin-Name: 52b03f045edf6fc29f9ba9a5cac53a59f0feb0eb

ext/misc/fileio.c

@@ -61,7 +61,6 @@ static void writefileFunc(
 ){
   FILE *out;
   const char *z;
-  int n;
   sqlite3_int64 rc;
   const char *zFile;
 
@@ -71,11 +70,9 @@ static void writefileFunc(
   if( out==0 ) return;
   z = (const char*)sqlite3_value_blob(argv[1]);
   if( z==0 ){
-    n = 0;
     rc = 0;
   }else{
-    n = sqlite3_value_bytes(argv[1]);
-    rc = fwrite(z, 1, n, out);
+    rc = fwrite(z, 1, sqlite3_value_bytes(argv[1]), out);
   }
   fclose(out);
   sqlite3_result_int64(context, rc);