cleanup(phoneme): remove activeTierOnlyBoundaries leftovers from Phon… #29

Job	Run time
module-standalone (macos-14, arm64-osx, cpu, OFF)	1m 27s
module-standalone (windows-latest, x64-windows, dml, ON)	16m 14s
module-standalone (ubuntu-24.04, x64-linux, cpu, OFF)	2m 32s
	20m 13s

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