Update install_and_test.md

install_and_test.md

@@ -23,9 +23,6 @@ To run the C and python tests of the installed `hotwheels` components, run:
 python -m hotwheels.checkup hotwheels
 ```
 
-
-## Environment variables
-
 Here below some relevant environment variables to change hotwheels default settings:
 
 | Environment Variable | Description                                                                                           |