Fix seam in glyphs of Cyrillic Capital/Small Letter Zhwe.

[jmcwilliams403]

The solution was simply to make the mask have no overshoot (the visible ze-part glyph itself still has overshoot).
Also cleanup epsilon code using default values for left, right, and blend (also hook too, technically, although this pretends it's still needed).

Ꚅꚅ

Thin before:

Thin after:

Regular before:

Regular after:

Heavy before:

Heavy after: