Remove dead_stores HashSet and clean up pass #12636

Job	Run time
omnibus compilations, trigger	2s
omnibus compilations, #5	27m 31s
omnibus compilations, #11	27m 23s
omnibus compilations, #12	15m 56s
omnibus compilations, #4	28m 29s
omnibus compilations, #6	31m 25s
omnibus compilations, #8	30m 34s
omnibus compilations, #1	29m 43s
omnibus compilations, #3	42m 27s
omnibus compilations, #2	38m 28s
omnibus compilations, #9	30m 56s
omnibus compilations, #7	36m 30s
omnibus compilations, #10	31m 50s
omnibus compilations, result	5s
	6h 11m 19s

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