add timestamp field to uORB msgs; sync timestamp whenever possible

msg/templates/uorb/msg.cpp.template

@@ -61,7 +61,7 @@ topic_name = spec.short_name
 
 sorted_fields = sorted(spec.parsed_fields(), key=sizeof_field_type, reverse=True)
 struct_size, padding_end_size = add_padding_bytes(sorted_fields, search_path)
-topic_fields = ["uint64_t timestamp"]+["%s %s" % (convert_type(field.type), field.name) for field in sorted_fields]
+topic_fields = ["%s %s" % (convert_type(field.type), field.name) for field in sorted_fields]
 }@
 
 #include <cinttypes>

msg/templates/uorb/msg.h.template

@@ -110,8 +110,6 @@ struct __EXPORT @(uorb_struct) {
 #else
 struct @(uorb_struct) {
 #endif
-@# timestamp at the beginning of each topic is required for logger
-	uint64_t timestamp; // required for logger
 @print_parsed_fields()
 
 #ifdef __cplusplus