scrub: some left over fixes

These fixes were in intermediate merge commits intended to be squashed
into the PR that would have been merged after as it was rebased, and
some things that slipped through the cracks.

Remove conflict_skip map and per-commit skip check in check_one_commit,
commits are filtered ahead of time.

Remove some straggler /dev/null redirects

Author: nothingmuch

contrib/scrub-commit-history.sh

@@ -347,10 +347,6 @@ expect_fail_matches_checks() {
 # Appends to build_failed[] on failure.
 check_one_commit() {
   local hash=$1
-  if [ -n "${conflict_skip[$hash]:-}" ]; then
-    echo "  - $(fmt_commit "$hash") (skipped: conflict)"
-    return 0
-  fi
   if [ -n "${no_flake[$hash]:-}" ]; then
     if [ "$no_skip_missing" = true ]; then
       echo "  ✗ $(fmt_commit "$hash") (no flake.nix)"
@@ -441,9 +437,9 @@ echo "Checking for conflicts..."
 for idx in "${ordered[@]}"; do
   hash=${linear[$idx]}
   reason=""
-  if git ls-tree --name-only "$hash" 2>/dev/null | grep -qE '^\.jj(conflict-|-do-not-resolve)'; then
+  if git ls-tree --name-only "$hash" | grep -qE '^\.jj(conflict-|-do-not-resolve)'; then
     reason="jj conflict tree"
-  elif git grep -q -E '<{7}|>{7}|={7}' "$hash" -- 2>/dev/null; then
+  elif git grep -q -E '<{7}|>{7}|={7}' "$hash" --; then
     reason="conflict markers"
   fi
   if [ -n "$reason" ]; then
@@ -502,8 +498,8 @@ if git cat-file -e "$tip_hash:.gitignore" 2>/dev/null; then
   echo "Checking gitignore monotonicity..."
   for idx in "${ordered[@]}"; do
     hash=${linear[$idx]}
-    leaked=$(git ls-tree -r --name-only "$hash" 2>/dev/null |
-      git -C "$tmpdir/repo" check-ignore --stdin 2>/dev/null || true)
+    leaked=$(git ls-tree -r --name-only "$hash" |
+      git -C "$tmpdir/repo" check-ignore --stdin || true)
     if [ -n "$leaked" ]; then
       first=$(echo "$leaked" | head -1)
       count=$(echo "$leaked" | wc -l)