fix: drop redundant mise build task that shadowed mise-tasks/build

The added [tasks.build] in mise.toml overrode the pre-existing mise-tasks/build file, which builds both entire and git-remote-entire (the e2e canary/roger-roger scripts call 'mise run build' and need both). The file task already builds with no ldflags, so experimental commands are visible in mise builds without any addition here.