remove import of x/exp #5223

Job	Run time
prepare	4s
validate (lint, darwin/amd64)	2m 8s
validate (lint, darwin/arm64)	2m 11s
validate (lint, freebsd/amd64)	2m 9s
validate (lint, freebsd/arm64)	2m 6s
validate (lint, linux/amd64)	2m 12s
validate (lint, linux/arm64)	2m 7s
validate (lint, linux/s390x)	2m 17s
validate (lint, linux/ppc64le)	2m 15s
validate (lint, linux/riscv64)	2m 18s
validate (lint, openbsd/amd64)	2m 14s
validate (lint, openbsd/arm64)	2m 18s
validate (lint, windows/amd64)	2m 20s
validate (lint, windows/arm64)	2m 24s
validate (lint-gopls, darwin/amd64)	4m 0s
validate (lint-gopls, darwin/arm64)	3m 55s
validate (lint-gopls, freebsd/amd64)	4m 7s
validate (lint-gopls, freebsd/arm64)	3m 54s
validate (lint-gopls, linux/amd64)	3m 56s
validate (lint-gopls, linux/arm64)	4m 1s
validate (lint-gopls, linux/s390x)	3m 59s
validate (lint-gopls, linux/ppc64le)	4m 6s
validate (lint-gopls, linux/riscv64)	4m 23s
validate (lint-gopls, openbsd/amd64)	3m 50s
validate (lint-gopls, openbsd/arm64)	3m 50s
validate (lint-gopls, windows/amd64)	4m 0s
validate (lint-gopls, windows/arm64)	4m 7s
validate (validate-docs)	1m 42s
validate (validate-golangci)	29s
validate (validate-vendor)	41s
	1h 24m 3s

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