faces/totp: delete unused structure field

The TOTP watch face now keeps track of each key separately.
There is no need to compute offsets at runtime.

movement/watch_faces/complication/totp_face.h

@@ -60,7 +60,6 @@ typedef struct {
     uint8_t steps;
     uint32_t current_code;
     uint8_t current_index;
-    uint8_t current_key_offset;
 } totp_state_t;
 
 void totp_face_setup(movement_settings_t *settings, uint8_t watch_face_index, void ** context_ptr);