fix: remove stale plugin-trigger-* directories left behind by the rename

#1749 added the renamed trigger-* packages but the deletion side of the
git mv didn't make it into the commit, leaving both directory pairs on
main while pnpm-lock.yaml only knows the new names — every
frozen-lockfile install on CI fails. Remove the stale originals.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: os-zhuang