Configuration exists and is documented on config.inc.php
// This can help to avoid performance problems.
// Controls what happens on right frame when user clicks on a testsuite on tree.
// ENABLED -> show all test cases presents on test suite and children test suite.
// DISABLED -> nothing happens, to execute a test case you need to click on test case
$tlCfg->exec_cfg->show_testsuite_contents = DISABLED;