lapd: Remove unused variable t200_start in lapd_acknowledge.

lapd_core.c: In function 'lapd_acknowledge':
lapd_core.c:710:38: warning: variable 't200_start' set but not used [-Wunused-but-set-variable]
diff --git a/src/gsm/lapd_core.c b/src/gsm/lapd_core.c
index fb79a2f..96099ed 100644
--- a/src/gsm/lapd_core.c
+++ b/src/gsm/lapd_core.c
@@ -707,7 +707,7 @@
 {
 	struct lapd_datalink *dl = lctx->dl;
 	uint8_t nr = lctx->n_recv;
-	int s = 0, rej = 0, t200_reset = 0, t200_start = 0;
+	int s = 0, rej = 0, t200_reset = 0;
 	int i, h;
 
 	/* supervisory frame ? */
@@ -758,7 +758,6 @@
 		if (dl->tx_hist[sub_mod(dl->v_send, 1, dl->range_hist)].msg) {
 			LOGP(DLLAPD, LOGL_INFO, "start T200, due to unacked I "
 				"frame(s)\n");
-			t200_start = 1;
 			lapd_start_t200(dl);
 		}
 	}