test: remove unneeded flag check in test-vm-memleak

The `common` module checks that necessary flags are being used, so a
check in the test itself is no longer necessary.

PR-URL: https://github.com/nodejs/node/pull/34528


Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>