Follow-up to #1223. The hand-written FLAGS block in `lark-cli --help`
restated leaf-command flags at the root level — flags that are not
registered on the root command (they error "unknown flag" there). Even
trimmed to an illustrative example list, it duplicated information Cobra's
per-command `--help` already renders authoritatively, and any static list
in root help drifts from the real per-command flag sets over time.
Drop the section entirely: Cobra's per-command `Flags:` output is the
single source of truth. `USAGE:`/`EXAMPLES:` still show flags in context,
and the `Flags:` block at the bottom of root help lists the actual root
flags. Also removes the now-obsolete TestRootLong_FlagsSectionPointsToCommandHelp.