build: use golangci-lint (#20295)

* build: use golangci-lint

This changes build/ci.go to download and run golangci-lint instead
of gometalinter.

* core/state: fix unnecessary conversion

* p2p/simulations: fix lock copying (found by go vet)

* signer/core: fix unnecessary conversions

* crypto/ecies: remove unused function cmpPublic

* core/rawdb: remove unused function print

* core/state: remove unused function xTestFuzzCutter

* core/vm: disable TestWriteExpectedValues in a different way

* core/forkid: remove unused function checksum

* les: remove unused type proofsData

* cmd/utils: remove unused functions prefixedNames, prefixFor

* crypto/bn256: run goimports

* p2p/nat: fix goimports lint issue

* cmd/clef: avoid using unkeyed struct fields

* les: cancel context in testRequest

* rlp: delete unreachable code

* core: gofmt

* internal/build: simplify DownloadFile for Go 1.11 compatibility

* build: remove go test --short flag

* .travis.yml: disable build cache

* whisper/whisperv6: fix ineffectual assignment in TestWhisperIdentityManagement

* .golangci.yml: enable goconst and ineffassign linters

* build: print message when there are no lint issues

* internal/build: refactor download a bit

internal/build/archive.go

@@ -213,11 +213,10 @@ func ExtractTarballArchive(archive string, dest string) error {
 		target := filepath.Join(dest, header.Name)
 
 		switch header.Typeflag {
-		case tar.TypeDir:
-			if err := os.MkdirAll(target, 0755); err != nil {
+		case tar.TypeReg:
+			if err := os.MkdirAll(filepath.Dir(target), 0755); err != nil {
 				return err
 			}
-		case tar.TypeReg:
 			file, err := os.OpenFile(target, os.O_CREATE|os.O_RDWR, os.FileMode(header.Mode))
 			if err != nil {
 				return err