Fix build.

Forgot to delete a line.

Change-Id: Ia1fb2904398816d495045dc237337f0be5b09272
Reviewed-on: https://boringssl-review.googlesource.com/7250
Reviewed-by: Steven Valdez <svaldez@google.com>
Reviewed-by: David Benjamin <davidben@google.com>

crypto/modes/ctr.c

@@ -143,7 +143,6 @@ void CRYPTO_ctr128_encrypt(const uint8_t *in, uint8_t *out, size_t len,
 /* increment upper 96 bits of 128-bit counter by 1 */
 static void ctr96_inc(uint8_t *counter) {
   uint32_t n = 12, c = 1;
-  uint8_t c;
 
   do {
     --n;