Remove some unnecessary copies #763

Job	Run time
build_attest_all (buildconfigs/key_xor_test_app.sh)	41m 4s
build_attest_all (buildconfigs/oak_client_android_app.sh)	49m 39s
build_attest_all (buildconfigs/oak_containers_agent.sh)	35m 9s
build_attest_all (buildconfigs/oak_containers_kernel.sh)	33m 51s
build_attest_all (buildconfigs/oak_containers_orchestrator.sh)	48m 53s
build_attest_all (buildconfigs/oak_containers_stage1.sh)	47m 28s
build_attest_all (buildconfigs/oak_containers_syslogd.sh)	49m 48s
build_attest_all (buildconfigs/oak_containers_system_image.sh)	48m 51s
build_attest_all (buildconfigs/oak_containers_nvidia_system_image.sh)	52m 40s
build_attest_all (buildconfigs/oak_echo_enclave_app.sh)	40m 38s
build_attest_all (buildconfigs/oak_echo_raw_enclave_app.sh)	41m 23s
build_attest_all (buildconfigs/oak_functions_enclave_app.sh)	41m 50s
build_attest_all (buildconfigs/oak_functions_insecure_enclave_app.sh)	41m 53s
build_attest_all (buildconfigs/oak_orchestrator.sh)	40m 56s
build_attest_all (buildconfigs/oak_restricted_kernel_simple_io_init_rd_wrapper_bin.sh)	41m 51s
build_attest_all (buildconfigs/stage0_bin.sh)	41m 28s
build_attest_all (buildconfigs/stage0_bin_tdx.sh)	41m 16s
	12h 18m 38s

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