cleanup enableProfilerNestedUpdateScheduledHook feature flag

[noahlemen]

Summary

Looks like this was added years ago for instrumentation at meta that never ended up rolling out. Should be safe to clean up.

How did you test this change?

yarn test

[react-sizebot]

Comparing: 64f354cf27a17c4e5b0dfcd908e47940cf947771...6f0dc94df99a4ec0f703b304765e4aab684bb640

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.min.js	=	177.10 kB	177.10 kB	=	55.20 kB	55.20 kB
oss-experimental/react-dom/cjs/react-dom.production.min.js	=	177.64 kB	177.64 kB	=	55.53 kB	55.53 kB
facebook-www/ReactDOM-prod.classic.js	=	594.34 kB	594.34 kB	=	104.96 kB	104.96 kB
facebook-www/ReactDOM-prod.modern.js	=	577.60 kB	577.60 kB	=	102.02 kB	102.02 kB
test_utils/ReactAllWarnings.js	Deleted	66.60 kB	0.00 kB	Deleted	16.28 kB	0.00 kB

Significant size changes

Includes any change greater than 0.2%:

Expand to show

Name	+/-	Base	Current	+/- gzip	Base gzip	Current gzip
test_utils/ReactAllWarnings.js	Deleted	66.60 kB	0.00 kB	Deleted	16.28 kB	0.00 kB

Generated by :no_entry_sign: dangerJS against 6f0dc94df99a4ec0f703b304765e4aab684bb640