STORM-122 FIXED Clean up obsolete floaters and related dead code

Removed obsolete XUI files:

floater_activeim.xml
floater_customize.xml
floater_device_settings.xml
floater_first_time_tip.xml
floater_im.xml
floater_my_friends.xml
floater_outfit_save_as.xml
floater_preview_classified.xml
floater_preview_event.xml
floater_preview_gesture_info.xml
floater_preview_gesture_shortcut.xml
floater_preview_gesture_steps.xml
floater_statistics.xml
floater_wearable_save_as.xml
panel_audio_device.xml
panel_friends.xml
panel_groups.xml
panel_nearby_chat.xml
panel_online_status.xml
panel_region_general_layout.xml

Killed obsolete LLFloaterVoiceDeviceSettings class, and moved LLPanelVoiceDeviceSettings into its own appropriately named files.