Remove unneeded cast to void in lowbd_fwd_txfm2d_4x8_neon

The `stride` parameter is used in the function body, so there is no need
to suppress the unused parameter warning here.

Change-Id: Icf0eb8e2e232d70a7e7c5f9aa82f75a375dd5a4b

av1/encoder/arm/neon/av1_fwd_txfm2d_neon.c

diff --git a/av1/encoder/arm/neon/av1_fwd_txfm2d_neon.c b/av1/encoder/arm/neon/av1_fwd_txfm2d_neon.c
index 311af05..7d24e21 100644
--- a/av1/encoder/arm/neon/av1_fwd_txfm2d_neon.c
+++ b/av1/encoder/arm/neon/av1_fwd_txfm2d_neon.c
@@ -1581,7 +1581,6 @@
 
 static void lowbd_fwd_txfm2d_4x8_neon(const int16_t *input, int32_t *output,
                                       int stride, TX_TYPE tx_type, int bd) {
-  (void)stride;
   (void)bd;
   int16x4_t buf0[8];
   int16x8_t buf1[8];