Remove `CondaEnvFileService` since we can get the same data from `conda info`

[luabud]

Based on the spike this #6882

It is safe to remove CondaEnvFileService entirely. Relying on conda info or conda list should work to get all conda environments. CondaEnvFileService was added to read ~/.conda/environemnts.txt to get the environments. This was because at that time conda info or conda list was not providing the full list of environments.

EDIT

The spike was done only for Linux and Windows, we assumed that linux behavior will be same as mac, which is not true. CondaEnvFileService is needed there for conda version 4.6.14.