Remove Compiler.depths parameter

This is no longer necessary with the depths array tracking and adds compiler overhead.
Remove unused vars and add jshint checking
Fix remaining depth arg
Avoid unnecessary this. reference
Track depths on deduped children

Fixes a very specific error case where deduped children won’t receive the depths object due to it being omitted by the caller when optimizing.

Fixes #926
Update fix for #926 for 3.0 codeline