Make mergebot message clearer when starting a new merge (#86311)
Modifying how the merge started message appears to make it more readable.
Also removing some deprecated v1 land checks messages
Old:
<img width="917" alt="image" src="https://user-images.githubusercontent.com/4468967/194150650-c9e384a3-d13c-40aa-975d-f43853790603.png">
New:
<img width="933" alt="image" src="https://user-images.githubusercontent.com/4468967/194151507-a5900cd5-5711-4cab-9447-c2cc6ed0d7b5.png">
Pull Request resolved: https://github.com/pytorch/pytorch/pull/86311
Approved by: https://github.com/malfet, https://github.com/huydhn
