d8: Remove experimental notice from stderr

[ptomato]

If you invoke d8 with any --harmony flags, it prints a warning to stderr that you are using experimental technologies. Remove this warning from the captured stderr, because it's just noise - if you are running d8 with a --harmony flag via eshost, you probably know what you are doing.

Additionally, non-empty stderr makes test262harness think the test has failed, so it's currently impossible to run test262 tests for a --harmony feature.

[gibson042]

Is this actually still an issue at all?

$ ~/.esvu/bin/v8 </dev/null
V8 version 13.7.67
d8> 
$ ~/.esvu/bin/v8 --harmony -e 'print("loaded")'
loaded

[ptomato]

Apparently is still an issue if you use a more specific --harmony flag:

~/.esvu/bin/v8 --harmony-temporal
V8 is running with experimental features enabled. Stability and security will suffer.
V8 version 13.7.67
d8>