Don't include assert.h from public header file

Signed-off-by: Xiang Xiao <xiaoxiang@xiaomi.com>

wireless/bluetooth/bt_att.c

@@ -48,6 +48,7 @@
 
 #include <stdbool.h>
 #include <string.h>
+#include <assert.h>
 #include <errno.h>
 #include <debug.h>
 

wireless/bluetooth/bt_conn.c

@@ -51,6 +51,7 @@
 #include <stdlib.h>
 #include <fcntl.h>
 #include <string.h>
+#include <assert.h>
 #include <errno.h>
 #include <debug.h>
 

wireless/bluetooth/bt_hcicore.c

@@ -53,6 +53,7 @@
 #include <fcntl.h>
 #include <time.h>
 #include <sched.h>
+#include <assert.h>
 #include <errno.h>
 #include <debug.h>