chore(lookups): remove empty E2E test CSV fixtures

Two empty CSV files (2 bytes each, header-only-with-just-newline)
were left in lookups/ from E2E test runs:

  - DR_APPROVAL_TEST_1.csv (Apr  3, build 575-era approval-gate test)
  - test_gated_csv.csv     (Apr  5, build 580-era gate test)

DR_APPROVAL_TEST_1.csv was already excluded from the .spl by
package.sh's "lookups/DR*" exclusion rule, but still tripped
scripts/validate.sh because validate scans the source tree state,
not the package output.

test_gated_csv.csv (no DR prefix) WAS being included in the .spl —
shipping a degenerate CSV to release users would have caused first-
load errors in any consumer that parses lookups/ blindly.

Surfaced by the 2026-05-13 Sigstore signing dry-run: validate failed
on "empty or missing header" for both files before package + sign.

Not removing the other 9 test CSVs (DR_BROWSER_TEST, DR_E2E_ADMIN,
DR_STRESS_2000x100, etc.) in this commit; they have valid headers
and pass validate. The lookups/DR* package.sh exclusion already
prevents them from shipping in the .spl, so they're invisible to
release users — broader cleanup is separate work.

Author: wildleo91