Error on unsupported -v

[lawcho]

Closes #7190

[lawcho]

Closing due to this use case:

• Agda built without DEBUG
• Agda invoked with -v tc.debug:5
• On code containing debugPrint msg 5 ("tc" :: "debug" :: [])

Behavior before this PR:

• Hard-coded logging on tc.debug:5 doesn't run
• debugPrint msg 5 ("tc" :: "debug" :: []) does run

Behavior after this PR:

• Agda crashes at arg-parse time.

Discussed at AIMXXXVIII with @UlfNorell -- the old behavior is desired