Remove remaining uses of `buttercup--mark-stackframe' #337

Job	Run time
Build and test (24.4)	29s
Build and test (24.5)	30s
Build and test (25.1)	29s
Build and test (25.2)	28s
Build and test (25.3)	29s
Build and test (26.1)	32s
Build and test (26.2)	31s
Build and test (26.3)	26s
Build and test (27.1)	31s
Build and test (28.1)	28s
Build and test (28.2)	30s
Build and test (29.1)	29s
Build and test (29.2)	40s
Build and test (29.3)	45s
Build and test (29.4)	44s
Build and test (release-snapshot)	41s
Build and test (snapshot)	30s
	9m 12s

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