Preparation to BraveConfirmInfoBar refactor
Deleted unused code to make refactoring more easier.
No production delegate ever used BUTTON_EXTRA.
Remove it together with the GetButtons override, GetButtonsOrder, IsProminent, and
ExtraButtonPressed virtuals that only existed to support it.
Delete the chromium_src patch that injected BUTTON_EXTRA into upstream's enum.
Cleaned up dead code from confirm_infobar.h overriding
Resolves - subtask of brave/brave-browser#48822
Simon Hong
fc1f49123e