🚮 Experiment sweep

Sweep experiments last flipped globally up to 2019-12-06T08:00:26.122Z:

- (ampproject#17012) `amp-access-iframe` (on)
- (ampproject#24810) `amp-action-macro` (on)
- (ampproject#25480) `amp-mega-menu` (on)
- (ampproject#25516) `amp-nested-menu` (on)
- (ampproject#7403) `amp-playbuzz` (on)
- (ampproject#25170) `amp-sidebar-swipe-to-dismiss` (on)
- (ampproject#19140) `amp-story-responsive-units` (on)
- (ampproject#16678) `amp-story-v1` (on)
- (ampproject#16678) `chunked-amp` (on)
- (ampproject#25269) `fix-inconsistent-responsive-height-selection` (off)
- (ampproject#21058) `fixed-elements-in-lightbox` (on)
- (ampproject#9298) `pump-early-frame` (on)
- (ampproject#25512) `swg-gpay-native` (on)

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**⚠️ This changes Javascript source files**

The following may contain errors, and require intervention to remove superfluous conditionals:

- `extensions/amp-access/0.1/amp-access-source.js`
- `extensions/amp-access/0.1/test/test-amp-access-source.js`
- `extensions/amp-action-macro/0.1/amp-action-macro.js`
- `extensions/amp-action-macro/0.1/test/test-amp-action-macro.js`
- `extensions/amp-playbuzz/0.1/amp-playbuzz.js`
- `extensions/amp-playbuzz/0.1/test/test-amp-playbuzz.js`
- `extensions/amp-sidebar/0.1/amp-sidebar.js`
- `extensions/amp-sidebar/0.2/amp-sidebar.js`
- `extensions/amp-story/1.0/amp-story.js`
- `extensions/amp-story/1.0/test/test-amp-story.js`
- `src/runtime.js`
- `test/unit/test-runtime.js`