Revert "Ship enableFabricCompleteRootInCommitPhase (#32318)"

[jackpope]

This reverts commit 8759c5c / #32318

We discovered that the experiment setup for this was faulty and we need to re-run as a back test.

[react-sizebot]

Comparing: fcb4e0f...e76b0f8

Critical size changes

Includes critical production bundles, as well as any change greater than 2%:

Name	+/-	Base	Current	+/- gzip	Base gzip	Current gzip
oss-stable/react-dom/cjs/react-dom.production.js	=	6.68 kB	6.68 kB	+0.05%	1.83 kB	1.83 kB
oss-stable/react-dom/cjs/react-dom-client.production.js	=	515.71 kB	515.71 kB	=	92.09 kB	92.09 kB
oss-experimental/react-dom/cjs/react-dom.production.js	=	6.69 kB	6.69 kB	=	1.83 kB	1.83 kB
oss-experimental/react-dom/cjs/react-dom-client.production.js	=	562.25 kB	562.25 kB	=	100.08 kB	100.08 kB
facebook-www/ReactDOM-prod.classic.js	=	636.70 kB	636.70 kB	=	112.08 kB	112.08 kB
facebook-www/ReactDOM-prod.modern.js	=	627.02 kB	627.02 kB	=	110.49 kB	110.49 kB

Significant size changes

Includes any change greater than 0.2%:

Expand to show

Name	+/-	Base	Current	+/- gzip	Base gzip	Current gzip
react-native/implementations/ReactFabric-prod.js	=	359.35 kB	358.62 kB	=	62.51 kB	62.40 kB
react-native/implementations/ReactFabric-profiling.js	=	384.68 kB	383.86 kB	=	66.21 kB	66.11 kB

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