Retire the option of using DNS over HTTPS for unstoppable domains resolution

[yrliou]

Once we have L2 solution working, we should retire the option of using DNS over HTTPS for unstoppable domains and remove related codes.

See brave/brave-core#7702 for reference.

[yrliou]

We would like to do the same for ENS too. And we can remove the obsolete codes for supporting DoH option.

[yrliou]

@supermassive FYI, We also need to retire the option in Android at the same time too, see brave/brave-core#8520.

[kjozwiak]

The above requires 1.40.80 or higher for 1.40.x verification 👍

[srirambv]

Brave	1.40.80 Chromium: 102.0.5005.78 (Official Build) beta (64-bit)
Revision	df6dbb5a9fd82af3f567198af2eb5fb4876ef99c-refs/branch-heads/5005_59@{#3}
OS	☑️ Linux	☑️ Windows 11 Version 22H2 (Build 22621.1)	☑️ macOS Version 12.0.1 (Build 21C52)
Verified steps from brave/brave-core#13354 Verified if the setting was set to DNS over HTTPS, upgrading reset it back to Ask Verified UD and ENS still work correctly with Ethereum option.
Remove DoH upon upgrade	22149-Linux.mp4	22149-Windows.mov	22149-macOS.mov
Ask/UD
Ethereum

[srirambv]

Verification passed on Oppo Reno 5 with Android 12 running 1.40.105 x64 build

• Verified steps from brave/brave-core#13354
• Verified if the setting was set to DNS over HTTPS, upgrading reset it back to Ask
• Verified UD and ENS still work correctly with Ethereum option.

Remove DoH upon upgrade	Ask/UD /Ethereum Name Service
22419.Clean.-ARM.mp4	22419.Upgrade.-ARM.mp4