Replace common.Append (removed in #19665) with append(common.Copy(prev), ...)
to fix the build.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Remove 11 Go files and 1 readme that contain only a license header and
package declaration, only commented-out code, or document a package that
no longer exists. Follow-up to #19665.

- cl/transition/impl/funcmap/impl.go - entire Impl struct/methods in a
  block comment; only file in the package; no external references.
- cl/utils/time_test.go - both test bodies commented out.
- cmd/rpcdaemon/graphql/graph/model/test.go - just `package model`.
- cmd/sentinel/sentinelcli/flags/{flags,defaultFlags}.go - the whole
  package was empty (only these two files, neither imported anywhere).
- common/log/skip.go - just `package log`.
- db/integrity/receipts_no_duplicates_test.go - just `package integrity`.
- db/kv/temporal/historyv2/{changeset.go,readme.md} - the package was
  intentionally removed in #19665 but was accidentally re-introduced by
  a rebase artifact in #21124 (whose commit message is entirely about
  state-test fixes and never mentions historyv2); the codebase has zero
  references to it.
- db/state/reconst.go - orphan `package state` declaration in a 66-file
  package.
- execution/tracing/tracers/tracer.go - just `package tracers`; the
  sibling `tracers.go` is the real file.
- execution/tracing/tracers/logger/logger2_test.go - test body fully
  commented out.

Intentionally kept: doc.go files (godoc), gen.go/mockgen.go/abi.go
(//go:generate hosts), node/interfaces/*/keep.go (sub-module package
markers), and execution/commitment/bin_patricia_hashed{,_test}.go
(commented-out reference implementation worth preserving).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

## Summary

Remove 11 Go files and 1 readme that contain only a license header and
package declaration, only commented-out code, or document a package that
no longer exists. Follow-up to erigontech#19665.

### Removed

- `cl/transition/impl/funcmap/impl.go` — entire `Impl` struct/methods in
a block comment; only file in the package; no external references.
- `cl/utils/time_test.go` — both test bodies commented out.
- `cmd/rpcdaemon/graphql/graph/model/test.go` — just `package model`.
- `cmd/sentinel/sentinelcli/flags/{flags,defaultFlags}.go` — the whole
package was empty (only these two files, neither imported anywhere).
- `common/log/skip.go` — just `package log`.
- `db/integrity/receipts_no_duplicates_test.go` — just `package
integrity`.
- `db/kv/temporal/historyv2/{changeset.go,readme.md}` — the package was
intentionally removed in erigontech#19665 but was accidentally re-introduced by a
rebase artifact in erigontech#21124 (whose commit message is entirely about
state-test fixes and never mentions historyv2); the codebase has zero
references to it.
- `db/state/reconst.go` — orphan `package state` declaration in a
66-file package.
- `execution/tracing/tracers/tracer.go` — just `package tracers`; the
sibling `tracers.go` is the real file.
- `execution/tracing/tracers/logger/logger2_test.go` — test body fully
commented out.

### Intentionally kept

Several other files matched "empty-except-package-and-comments" but
serve real purposes and were left alone:

- `doc.go` files in `common/log/v3/{,term/}`, `execution/rlp/`,
`execution/vm/{,runtime/}`, `p2p/dnsdisc/`, `node/{,app/workerpool/}`,
`rpc/` — godoc package documentation.
- `gen.go` / `mockgen.go` / `abi.go` files in `cmd/pics/contracts/`,
`txnprovider/shutter/internal/contracts/`, `execution/tests/contracts/`,
`execution/state/contracts/`, `rpc/jsonrpc/contracts/`,
`execution/protocol/rules/aura/auraabi/`,
`node/gointerfaces/{sentryproto,remoteproto,downloaderproto}/` —
`//go:generate` hosts.
-
`node/interfaces/{,p2psentinel/,types/,web3/,downloader/,txpool/,execution/,p2psentry/,remote/}keep.go`
— package markers for the `.proto`-only sub-module rooted at
`node/interfaces/` (has its own `go.mod`).
- `execution/commitment/bin_patricia_hashed{,_test}.go` — commented-out
reference implementation worth preserving for future work.

## Test plan

- [x] `make erigon integration` — clean build.
- [x] `make lint` — `0 issues.`
- [ ] CI green.

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>