build: enable gosimple linter (#15593)

build/ci.go

@@ -335,7 +335,7 @@ func doLint(cmdline []string) {
 	build.MustRunCommand(filepath.Join(GOBIN, "gometalinter.v1"), append(configs, packages...)...)
 
 	// Run slow linters one by one
-	for _, linter := range []string{"unconvert"} {
+	for _, linter := range []string{"unconvert", "gosimple"} {
 		configs = []string{"--vendor", "--deadline=10m", "--disable-all", "--enable=" + linter}
 		build.MustRunCommand(filepath.Join(GOBIN, "gometalinter.v1"), append(configs, packages...)...)
 	}