build: remove legacy rnjs setup #7707

Job	Run time
lint	24s
build	16s
e2e_windows (windows-2025, 22, npm, 0)	23s
e2e_windows (windows-2025, 22, npm, 2)	15s
e2e_windows (windows-2025, 22, esbuild, 0)	24s
e2e_windows (windows-2025, 22, npm, 1)	15s
e2e_windows (windows-2025, 22, npm, 3)	15s
e2e_windows (windows-2025, 22, npm, 5)	14s
e2e_windows (windows-2025, 22, npm, 4)	14s
e2e_windows (windows-2025, 22, esbuild, 1)	17s
e2e_windows (windows-2025, 22, esbuild, 2)	13s
e2e_windows (windows-2025, 22, esbuild, 4)	14s
e2e_windows (windows-2025, 22, esbuild, 5)	13s
e2e_windows (windows-2025, 22, esbuild, 3)	25s
Browser Compatibility Tests	1s
publish-snapshots	1s
test	1s
e2e-snapshots	1s
e2e	1s
e2e-package-managers	1s
	4m 8s

Provide feedback