Remove calls to APIs deprecated in V8 12.6

[ajklein]

Both updates are trivial:

• v8::ScriptOrigin's constructor no longer takes an Isolate (it was already unused)
• v8::SafeForTerminationScope and the Isolate creation param only_terminate_in_safe_scope are gone (they were already no-ops)

See v8#185 for the fixes I made to keep V8's CI happy.

cc @joyeecheung

[targos]

Thanks for the heads up! I opened #52996 with your changes.