Eliminate non-inclusive language from AMP's source code

In the interest of making AMP development more [meaningful and inclusive](https://sfconservancy.org/news/2020/jun/23/gitbranchname/), we are in the midst of an effort to rectify parts of our infrastructure and source code that use non-inclusive language. See https://github.com/ampproject/amphtml/issues/32195 for more info.

This issue is being filed as a catch-all. I will follow up with a few comments, one per major instance I can find. If you're reading this and find a spot that I missed, please add a new comment!

The plan is to tag the WGs who own this code so they can drive fixes (where needed) at leisure. Please add a thumbs-up reaction to individual comments as acknowledgement, and back-link any fixes to this issue.

We can close this issue when all instances have been accounted for.

Review the comments on this issue and the linked issue #32195 to identify the reported instances and the WGs that own them. Check each instance with its owning WG, make any needed fix, and finish when all instances are accounted for and fixes are back-linked here.

Written by the indexing model from the issue text.