iOS: Remove iOS 12 preprocessor checks

The current minimum-supported Xcode (10.1) includes the iOS 12.1 SDK, so
APIs from iOS 12 will always be available.

modules/juce_core/native/juce_BasicNativeHeaders.h

@@ -28,7 +28,7 @@
 #if JUCE_MAC || JUCE_IOS
 
  #if JUCE_IOS
-  #if JUCE_MODULE_AVAILABLE_juce_opengl && defined (__IPHONE_12_0) && __IPHONE_OS_VERSION_MAX_ALLOWED >= __IPHONE_12_0
+  #if JUCE_MODULE_AVAILABLE_juce_opengl
    #define GLES_SILENCE_DEPRECATION 1
   #endif
 

modules/juce_gui_basics/native/juce_ios_UIViewComponentPeer.mm

@@ -773,7 +773,6 @@ MultiTouchMapper<UITouch*> UIViewComponentPeer::currentTouches;
 {
     [super traitCollectionDidChange: previousTraitCollection];
 
-   #if defined (__IPHONE_12_0) && __IPHONE_OS_VERSION_MAX_ALLOWED >= __IPHONE_12_0
     if (@available (iOS 12.0, *))
     {
         const auto wasDarkModeActive = ([previousTraitCollection userInterfaceStyle] == UIUserInterfaceStyleDark);
@@ -782,7 +781,6 @@ MultiTouchMapper<UITouch*> UIViewComponentPeer::currentTouches;
             [[NSNotificationCenter defaultCenter] postNotificationName: UIViewComponentPeer::getDarkModeNotificationName()
                                                                 object: nil];
     }
-   #endif
 }
 
 - (BOOL) isAccessibilityElement

modules/juce_gui_basics/native/juce_ios_Windowing.mm

@@ -691,10 +691,8 @@ bool Desktop::canUseSemiTransparentWindows() noexcept
 
 bool Desktop::isDarkModeActive() const
 {
-   #if defined (__IPHONE_12_0) && __IPHONE_OS_VERSION_MAX_ALLOWED >= __IPHONE_12_0
     if (@available (iOS 12.0, *))
         return [[[UIScreen mainScreen] traitCollection] userInterfaceStyle] == UIUserInterfaceStyleDark;
-   #endif
 
     return false;
 }