The resource pack attached to MC-214686 offers a complete fix for this issue. Mojang have my full permission to (and are encouraged to) replace the affected vanilla model files with the contents of the resource pack.

The bug

Redstone repeater models define faces for the bottoms of unlit redstone torches, as well as the bottom of locks for locked repeaters, despite these never being visible without clipping into the repeater itself. Powered torches correctly omit such faces due to not using a single cuboid.

How to reproduce

1. Place down an unpowered redstone repeater
2. Enter Spectator mode
3. Fly into the repeater such that the bottoms of the torches are in view

Expected behaviour

The unpowered torches would not have any bottom faces defined since such faces are never possible to see in normal gameplay.

Actual behaviour

These bottom faces are defined anyway, bloating the model file and forcing the game to render useless faces.

How to fix

The resource pack attached to MC-214686 fixes this issue completely.