[Infra Alerting UI] Audit new EUI Borealis theme (elastic#205142)

## Summary
It fixes elastic#205052 by 
- Remapping the vis color for the Infra rule preview chart. This is a
temporary solution because the current is not visible, so we are waiting
for @maciejforcone inputs.
- Deleting the unused Expression chart

x-pack/solutions/observability/plugins/infra/common/color_palette.test.ts

@@ -33,7 +33,7 @@ describe('Color Palette', () => {
   });
   describe('colorTransformer()', () => {
     it('should just work', () => {
-      expect(colorTransformer(Color.color0)).toBe('#6092C0');
+      expect(colorTransformer(Color.color0)).toBe('#54B399');
     });
   });
 });

x-pack/solutions/observability/plugins/infra/common/color_palette.ts

@@ -28,16 +28,19 @@ export type Palette = {
 const euiPalette = euiPaletteColorBlind();
 
 export const defaultPalette: Palette = {
-  [Color.color0]: euiPalette[1], // (blue)
-  [Color.color1]: euiPalette[2], // (pink)
-  [Color.color2]: euiPalette[0], // (green-ish)
-  [Color.color3]: euiPalette[3], // (purple)
-  [Color.color4]: euiPalette[4], // (light pink)
-  [Color.color5]: euiPalette[5], // (yellow)
-  [Color.color6]: euiPalette[6], // (tan)
-  [Color.color7]: euiPalette[7], // (orange)
-  [Color.color8]: euiPalette[8], // (brown)
-  [Color.color9]: euiPalette[9], // (red)
+  // TODO: Waiting for the designer input on the colors mapping
+  // As a temp solution, in the old palette, colors 0..3 are the dark colors, 4..6 are the light colors and 7..9 dark again
+  // I followed the same pattern here for the new palette
+  [Color.color0]: euiPalette[0],
+  [Color.color1]: euiPalette[2],
+  [Color.color2]: euiPalette[4],
+  [Color.color3]: euiPalette[6],
+  [Color.color4]: euiPalette[1],
+  [Color.color5]: euiPalette[3],
+  [Color.color6]: euiPalette[5],
+  [Color.color7]: euiPalette[8],
+  [Color.color8]: euiPalette[9],
+  [Color.color9]: euiPalette[7],
 };
 
 export const createPaletteTransformer = (palette: Palette) => (color: Color) => palette[color];