Cleanup ampdoc-fie experiment

[dvoytenko]

See launch in #22734

TODO for cleanup:

• Remove FriendlyIframeEmbedLegacy
• FriendlyIframeEmbed make ampdoc non-nullable and update the code accordingly.
• cleanup ampdoc service lookup
• Remove EmbeddableService.installInEmbedWindow interface.
• Remove installServiceInEmbedScope function.
• Remove opt_win, opt_root, etc arguments from Bind, AmpGwdRuntimeService, HiddenObserver, Action, StandardActions, Navigation, Url, and other embeddable services. (See Introduce ampdoc on a FIE level #22493 for some examples).
• Remove the getExistingServiceForDocInEmbedScope.
• Remove the installStylesLegacy.

[zhouyx]

cc @ampproject/wg-ads Does this mean that FIE will have its own instance of ampdoc in the future?

[dvoytenko]

yes