Drop confusing commented out code in pystrtod.c (GH-6072) (GH-9588)

Fix the following warning:

Python/pystrtod.c: In function 'format_float_short':
Python/pystrtod.c:1007:13: warning: 'strncpy' output truncated before terminating nul copying 3 bytes from a string of the same length [-Wstringop-truncation]
             strncpy(p, "ERR", 3);

(cherry picked from commit 9fb84157)

Python/pystrtod.c

@@ -1004,8 +1004,6 @@ format_float_short(double d, char format_code,
         else {
             /* shouldn't get here: Gay's code should always return
                something starting with a digit, an 'I',  or 'N' */
-            strncpy(p, "ERR", 3);
-            p += 3;
             assert(0);
         }
         goto exit;