Remove unused `color_saturation` parameter

Needs https://github.com/koreader/koreader-base/pull/1751

frontend/device/pocketbook/device.lua

@@ -598,7 +598,6 @@ local PocketBook632 = PocketBook:extend{
 local PocketBook633 = PocketBook:extend{
     model = "PBColor",
     display_dpi = 300,
-    color_saturation = 1.5,
     hasColorScreen = yes,
     canHWDither = yes, -- Adjust color saturation with inkview
     canUseCBB = no, -- 24bpp
@@ -672,7 +671,6 @@ local PocketBook740_2 = PocketBook:extend{
 local PocketBook741 = PocketBook:extend{
     model = "PBInkPadColor",
     display_dpi = 300,
-    color_saturation = 1.5,
     hasColorScreen = yes,
     canHWDither = yes, -- Adjust color saturation with inkview
     canUseCBB = no, -- 24bpp
@@ -689,7 +687,6 @@ end
 local PocketBook743C = PocketBook:extend{
     model = "PBInkPadColor2",
     display_dpi = 300,
-    color_saturation = 1.5,
     hasColorScreen = yes,
     canHWDither = yes, -- Adjust color saturation with inkview
     canUseCBB = no, -- 24bpp
@@ -708,7 +705,6 @@ local PocketBook743K3 = PocketBook:extend{
     model = "PBInkPadColor3",
     display_dpi = 300,
     viewport = Geom:new{x=3, y=2, w=1395, h=1864},
-    color_saturation = 1.5,
     hasColorScreen = yes,
     canHWDither = yes, -- Adjust color saturation with inkview
     canUseCBB = no, -- 24bpp
@@ -735,7 +731,6 @@ local PocketBook743G = PocketBook:extend{
 local PocketBookColorLux = PocketBook:extend{
     model = "PBColorLux",
     display_dpi = 125,
-    color_saturation = 1.5,
     hasColorScreen = yes,
     canHWDither = yes, -- Adjust color saturation with inkview
     canUseCBB = no, -- 24bpp