Deprecate and clean up the ALP related code

ALP (AMP landing page) was an AMP solution to eliminate the ad landing page redirection that many ad implementations used to have for click tracking purpose.

To my knowledge, it hasn't been adopted by any ad network in production since launched in AMP (@cramforce @zhouyx correct me). It's also not publicly documented.

Nowadays, a better and universal solution would be to use the ping attribute of anchor tag. This feature is not needed anymore.

Recently, we found that some ALP logic might indirectly caused issue #32030 . To reduce system complexity, I propose we formally deprecate and clean up the code.

@kristoferbaxter @dvoytenko

Start by locating the ALP (AMP landing page) implementation and reviewing issue #32030 for the reported indirect effects. Determine which ALP code and related deprecation work are in scope; done means the unused feature is formally deprecated and its code is cleaned up without retaining the problematic logic.

Written by the indexing model from the issue text.