Remove libubootenv-tool from packagelists and put in the ts-uboot-env-configs task

[lionel]

Several packagelists contain libubootenv-tool. Now that we have a task that decides whether a build should contain U-Boot environment support (tasks: add set-fw-env-config to select a fw_env.config at firstboot #51), the decision to install that package should be controlled by a config parameter, e.g. by the selection of DS_COMPONENT_TS_UBOOT_CONFIGS.