Remove unnecessary calls to variation.draw()

snakview._setValue is the only method calling variation.value. It drawed the
variation three times per call. First, in snakview._updateVariation, then by
calling variation.value directly, and finally through snakview.draw.

The variation.value call in snakview._updateVariation is also unnecessary,
since snakview._setValue (only caller) immediately calls variation.value
afterwards.

Change-Id: I66c0f13d09cccec7096a4c08db3ebd860c4931c0
Merge "Remove unnecessary calls to variation.draw()"