Clean up env logging on initialization

[chriselion]

This was misleading, because we now never have brains at the start, only after an agent sends its actions.
old:

'Academy' started successfully!
Unity Academy name: Academy
        Number of Training Brains : 0
        Reset Parameters :

new:

INFO:mlagents.envs:
'Academy' started successfully!
Unity Academy name: Academy
        Reset Parameters : {}
INFO:mlagents.envs:Connected new brain:
Unity brain name: Hallway
        Number of Visual Observations (per agent): 0
        Camera Resolutions: []
        Vector Observation space size (per agent): 108
        Vector Action space type: discrete
        Vector Action space size (per agent): [5]
        Vector Action descriptions: 

Saw one user confused about it on discord, and there as an issue comment on it too: #2856 (comment)