Remove `CvdFlag` #477

Job	Run time
build-metapackage-deb-job	8m 13s
build-uboot-qemu-job	3m 30s
build-installer-iso-job	2m 41s
build-cuttlefish-deb-job / build-arm64-cuttlefish-deb-job	1h 48m 33s
test-install-metapackage-deb-job	9m 46s
test-install-cuttlefish-deb-job	9m 36s
	2h 22m 19s

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