Redundant accelerators were:
- <Primary><Shift>y on dialogs-mypaint-brushes and edit-strong-redo.
  Since the <Primary>z vs <Primary>y has quite a strong history for
  undo/redo actions, and dialogs-mypaint-brushes is quite new, let's
  unmap the latest.
- <shift>l on tools-seamless-clone and tools-unified-transform.
  Since the Seamless clone tool is still in the playground and we
  don't even know if it will make it out quite soon, let's give
  priority to the Unified Transform tool.