Unnecessary faces in fence connection models

Closely relates to MCPE-170446.

The bug

For parts of fences that connect to horizontally adjacent blocks, there are faces which are never visible without clipping into the block. These faces can be removed, and they do not exist in Java Edition.

How to reproduce

1. Place a fence
2. Place a solid block next to it
3. Enter Spectator mode
4. Fly inside of the post

Expected results

The two faces of the parts of the fence extending out from the post (directly opposite the block) would not be visible from inside of the wall post.

Actual results

They are.

How to fix

Remove these two faces.