chore: delete unused npm lockfile impl in go (#4605)

### Description

Now that we've been shipping Go code that calls Rust for a bit and the
Rust lockfile implementation hasn't seen any major issues, I feel
comfortable deleting the unused Go NPM lockfile code. If issues to crop
up, this code is just a `git revert` away.

### Testing Instructions

Rust unit tests and integration tests.

cli/internal/lockfile/lockfile.go

@@ -61,6 +61,19 @@ func (p ByKey) Less(i, j int) bool {
 
 var _ (sort.Interface) = (*ByKey)(nil)
 
+// TransitiveClosure the set of all lockfile keys that pkg depends on
+func TransitiveClosure(
+	workspaceDir turbopath.AnchoredUnixPath,
+	unresolvedDeps map[string]string,
+	lockFile Lockfile,
+) (mapset.Set, error) {
+	if lf, ok := lockFile.(*NpmLockfile); ok {
+		// We special case as Rust implementations have their own dep crawl
+		return npmTransitiveDeps(lf, workspaceDir, unresolvedDeps)
+	}
+	return transitiveClosure(workspaceDir, unresolvedDeps, lockFile)
+}
+
 func transitiveClosure(
 	workspaceDir turbopath.AnchoredUnixPath,
 	unresolvedDeps map[string]string,

cli/internal/lockfile/npm_lockfile_rust.go → cli/internal/lockfile/npm_lockfile.go

@@ -1,6 +1,3 @@
-//go:build rust
-// +build rust
-
 package lockfile
 
 import (