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

PR-URL: #40945
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Richard Lau <rlau@redhat.com>

BUILDING.md

@@ -403,7 +403,7 @@ by providing the name of a subsystem:
 
 ```text
 $ make coverage-clean
-$ NODE_V8_COVERAGE=coverage/tmp tools/test.py -J --mode=release child-process
+$ NODE_V8_COVERAGE=coverage/tmp tools/test.py --mode=release child-process
 $ make coverage-report-js
 ```