Revert aarch64 fixup for ESR 60-based bundles with Tor Browser 9

We solved legacy/trac#31616 (moved) and legacy/trac#31140 (moved) by making sure the JIT prefs are not enabled via our security slider on aarch64.

We need to revert that for Tor Browser 9 and make sure that the security level is actually reset to low for those users whose level got set to custom due to the workaround we deployed. (Doing the latter might actually not be trivial).