[BUG] npm ls doesn't support depth

[darcyclarke]

Current Behavior:

Running npm ls <pkg> --depth=0 doesn't produce a filtered result of deps installed on disk

Expected Behavior:

Running npm ls <pkg> --depth=0 will show me just the top-level deps installed on disk (see npm@6.x)

Steps To Reproduce:

1. In any version npm@<=7.0.0-beta.12 ...
2. Run npm ls <pkg> --depth=0 ...
3. See same results as npm ls or even npm ls --all (there is no difference)

Environment:

• OS: OSX@10.15.6 (19G2021) - although I'm fairly positive this can be repro'd in all environments
• Node: 14.12.0
• npm: 7.0.0-beta.12