Remove DisplayInfo

[baconpaul]

Once we are on Juce no need for DisplayInfo

1. The backingstore depth won't be used any more
2. and juce::Display has everything we need

so eliminate this code completely rather than doing the fix below.

(was)
Right now, DisplayInfoMac and DIsplayInfoWin use the frame passed to them to find the display of the window and return the size of that window, meaning "max" works appropriately on multi-element displays. On Linux we don't do that; rather we just use the dimensions of the primary display. This means "max" works inconsistently on multi-display linux systems.

When @baconpaul wrote the rough cut of display size he commented this; @tank-trax later discovered it on his multi-monitor linux system.

[baconpaul]

hey this is done!