[Sensor] API merged ,removed and code refactoring.

[Sensor] API merged ,removed and code refactoring.

Changes are:
1) Functionality bt_hrp_sensor_update_heartrate_value
and bt_hrp_sensor_set_heartrate_value  are merged to
bt_hrp_sensor_set_heartrate_value .
2) removed bt_hrp_sensor_advertising_state_changed_cb
as this is not needed for application.
3) functionality of bt_hrp_sensor_start is merged
in bt_hrp_sensor_create .
4) functionality of bt_hrp_sensor_stop is merged
in bt_hrp_sensor_distroy.
5) Connected collector list in the sensor is removed ,
as sensor side connected is already managed by Gatt
server , so it was redundant and hence removed .
6) bt_hrp_sensor_unset_sensor_notification_state_change_cb
is removed, as is not needed by application .

Change-Id: I93ba307a9a9f06aa4a80a77571b502df61ffdd95
Signed-off-by: Abhishek Chandra <abhishek.ch@samsung.com>