doc: remove legacy -J test.py option from BUILDING.md

PR-URL: #42817
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Mestery <mestery@protonmail.com>
Reviewed-By: Darshan Sen <raisinten@gmail.com>

BUILDING.md

@@ -337,13 +337,13 @@ You can execute the entire suite of tests for a given subsystem
 by providing the name of a subsystem:
 
 ```text
-$ tools/test.py -J child-process
+$ tools/test.py child-process
 ```
 
 You can also execute the tests in a tests directory (such as `test/message`):
 
 ```text
-$ tools/test.py -J test/message
+$ tools/test.py test/message
 ```
 
 If you want to check the other options, please refer to the help by using