history: remove records without attached blobs at startup #4985

Job	Run time
build (windows/amd64)	1m 34s
build (freebsd/amd64)	1m 38s
test-freebsd-amd64	2m 36s
test-windows-amd64 (containerd, ./client)	3m 59s
test-windows-amd64 (containerd, ./cmd/buildctl)	2m 54s
test-windows-amd64 (containerd, ./worker/containerd)	3m 0s
test-windows-amd64 (containerd, ./solver)	3m 4s
test-windows-amd64 (containerd, ./frontend)	2m 36s
test-windows-amd64 (containerd, ./frontend/dockerfile)	30m 45s
test-windows-amd64 (./..., 1)	11m 51s
	1h 3m 57s

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