ci: delete the e2e-iter scratch lane

Built in May for one debugging session (iter/* branches, subset E2E),
never used since, and every run it ever had failed. An always-red lane
cannot be read: once a workflow is known-red, a new failure in it is
invisible. The full E2E matrix in the release pipeline covers the same
scenarios; recreate from history if a fast-iteration lane is wanted.

Author: ualtinok