Remove WindowSurfaceVk::swapImpl prototype.
Remove WindowSurfaceVk::swapImpl prototype.

This method was removed in a prior patch.

BUG=angleproject:1898

Change-Id: I2ab3c36bbef4ce6c978cd4c09cc191c4e7ff7991
Reviewed-on: https://chromium-review.googlesource.com/677547
Reviewed-by: Jamie Madill <7e492b4f1c8458024932de3ba475cbf015424c30@chromium.org>
Commit-Queue: Jamie Madill <7e492b4f1c8458024932de3ba475cbf015424c30@chromium.org>

MSOpenTech/angle,MSOpenTech/angle,ppy/angle,ppy/angle,ppy/angle,MSOpenTech/angle,ppy/angle,MSOpenTech/angle