Remove remaining uses of `buttercup--mark-stackframe' #329

Job	Run time
Build and test (24.4)	2m 20s
Build and test (24.5)	40s
Build and test (25.1)	32s
Build and test (25.2)	26s
Build and test (25.3)	36s
Build and test (26.1)	33s
Build and test (26.2)	44s
Build and test (26.3)	1m 42s
Build and test (27.1)	42s
Build and test (28.1)	27s
Build and test (28.2)	30s
Build and test (29.1)	28s
Build and test (29.2)	51s
Build and test (29.3)	50s
Build and test (29.4)	2m 25s
Build and test (release-snapshot)	1m 46s
Build and test (snapshot)	26s
	15m 58s

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