Why is my phone (L830) showing two phone options? How to go back to one app in the list?

[WPCentral Question]

I installed Windows 10 mobile (slow ring) build 10166 for a day but then rolled back to Windows 8.1...after almost a day I realised that there were two "Phone" apps in the app list and I can add both to the start screen, both showing different status of the sim/connection. (screenshots attached)

 

[brijendra_y07]

 

[broar94]

Merge the Numbers from settings