Cleanup: remove dc_user_device_t::trip

Since ff9506b21bbb9910256841dcb577bcb2e19047e8 the downloaders don't
add dives to a new trip and therefore the trip field of dc_user_device_t
became pointless. Remove it.

Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>

core/downloadfromdcthread.cpp

@@ -257,7 +257,6 @@ void show_computer_list()
 DCDeviceData::DCDeviceData()
 {
 	memset(&data, 0, sizeof(data));
-	data.trip = nullptr;
 	data.download_table = nullptr;
 	data.diveid = 0;
 	data.deviceid = 0;

core/libdivecomputer.h

@@ -38,7 +38,6 @@ typedef struct dc_user_device_t
 	dc_device_t *device;
 	dc_context_t *context;
 	dc_iostream_t *iostream;
-	struct dive_trip *trip;
 	int preexisting;
 	bool force_download;
 	bool libdc_log;