Remove ANDROID_frame_boundary extension

[purvisa-at-google-com]

As noted in b/241899902 We're disabling the ANDROID_frame_boundary extension for the Q3 22 release.

This disabling will be reverted at a future date once we've found a way of more robustly implementing the feature.

[yalcinmelihyasin]

Code wise there is not much to review here, therefore let's wait until our internal discussion is resolved.

[purvisa-at-google-com]

Superseded by https://github.com/google/agi/pull/1179