* Tests run in experimental mode by default
For local development, you usually want experiments enabled. Unless
the release channel is set with an environment variable, tests will
run with __EXPERIMENTAL__ set to `true`.
* Remove concurrent APIs from stable builds
Those who want to try concurrent mode should use the experimental
builds instead.
I've left the `unstable_` prefixed APIs in the Facebook build so we
can continue experimenting with them internally without blessing them
for widespread use.
* Turn on SSR flags in experimental build
* Remove prefixed concurrent APIs from www build
Instead we'll use the experimental builds when syncing to www.
* Remove "canary" from internal React version string
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