Revert "macOS: Force light theme on macOS 10.14+"

This does not really work: as soon as you build with
the 10.14 SDK you opt-in to having updated palette
management, which the Qt 5.11 series does not have.

This leaves app developers with two ways to opt-out
of dark mode:
 - Build with the 10.13 (or earlier) SDK.
 - Set NSRequiresAquaSystemAppearance in Info.plist

This reverts commit 04671a8.

Change-Id: I5c01b9965da45de914f699526ba0723837f36e1d
Reviewed-by: Tor Arne Vestbø <[email protected]>
Reviewed-by: Gabriel de Dietrich <[email protected]>

src/plugins/platforms/cocoa/qcocoaintegration.mm

@@ -70,12 +70,6 @@
 
 #include <IOKit/graphics/IOGraphicsLib.h>
 
-#if !QT_MACOS_PLATFORM_SDK_EQUAL_OR_ABOVE(__MAC_10_14)
-@interface NSApplication (MojaveForwardDeclarations)
-@property (strong) NSAppearance *appearance NS_AVAILABLE_MAC(10_14);
-@end
-#endif
-
 static void initResources()
 {
     Q_INIT_RESOURCE(qcocoaresources);
@@ -137,21 +131,6 @@ static void initResources()
     NSApplication *cocoaApplication = [QNSApplication sharedApplication];
     qt_redirectNSApplicationSendEvent();
 
-    if (__builtin_available(macOS 10.14, *)) {
-        // Disable dark appearance, unless the Info.plist or environment requests that it should be enabled
-        bool plistEnablesDarkAppearance = [[[NSBundle mainBundle] objectForInfoDictionaryKey:
-            @"NSRequiresAquaSystemAppearance"] boolValue];
-
-        bool hasEnvironmentRequiresAquaAppearance;
-        int environmentRequiresAquaAppearance = qEnvironmentVariableIntValue(
-            "QT_MAC_REQUIRES_AQUA_SYSTEM_APPEARANCE", &hasEnvironmentRequiresAquaAppearance);
-        bool environmentEnablesDarkAppearance = hasEnvironmentRequiresAquaAppearance
-            && environmentRequiresAquaAppearance == 0;
-
-        if (!(plistEnablesDarkAppearance || environmentEnablesDarkAppearance))
-            NSApp.appearance = [NSAppearance appearanceNamed:NSAppearanceNameAqua];
-    }
-
     if (qEnvironmentVariableIsEmpty("QT_MAC_DISABLE_FOREGROUND_APPLICATION_TRANSFORM")) {
         // Applications launched from plain executables (without an app
         // bundle) are "background" applications that does not take keybaord