Remove no-longer-needed fflushes of stderr

* src/gmalloc.c (mabort) [GC_MCHECK && !__GNU_LIBRARY__]:
* src/term.c (vfatal): Remove fflush (stderr) when it is now a
no-op because newline automatically flushes stderr.

src/gmalloc.c

@@ -2013,7 +2013,6 @@ mabort (enum mcheck_status status)
   __libc_fatal (msg);
 #else
   fprintf (stderr, "mcheck: %s\n", msg);
-  fflush (stderr);
   emacs_abort ();
 #endif
 }

src/term.c

@@ -4402,7 +4402,6 @@ vfatal (const char *str, va_list ap)
   vfprintf (stderr, str, ap);
   if (!(strlen (str) > 0 && str[strlen (str) - 1] == '\n'))
     fprintf (stderr, "\n");
-  fflush (stderr);
   exit (1);
 }