htp: minor cleanup to silence cppcheck warning

[src/app-layer-htp.c:1967] -> [src/app-layer-htp.c:1978]: (warning) \
    Possible null pointer dereference: tx - otherwise it is redundant \
    to check it against null.

src/app-layer-htp.c

@@ -1975,7 +1975,6 @@ static int HTPCallbackResponse(htp_tx_t *tx) {
     /* Unset the body inspection (if any) */
     hstate->flags &=~ HTP_FLAG_NEW_BODY_SET;
 
-    if (tx != NULL) {
     HtpTxUserData *htud = (HtpTxUserData *) htp_tx_get_user_data(tx);
     if (htud != NULL) {
         if (htud->tcflags & HTP_FILENAME_SET) {
@@ -1984,7 +1983,6 @@ static int HTPCallbackResponse(htp_tx_t *tx) {
             htud->tcflags &= ~HTP_FILENAME_SET;
         }
     }
-    }
 
     /* response done, do raw reassembly now to inspect state and stream
      * at the same time. */