macOS: Remove macOS 10.14 preprocessor checks

The current minimum-supported Xcode (10.1) includes the macOS 10.14.1
SDK, so APIs from macOS 10.14 will always be available.

modules/juce_core/native/juce_BasicNativeHeaders.h

@@ -41,7 +41,7 @@
   #import <MobileCoreServices/MobileCoreServices.h>
   #include <sys/fcntl.h>
  #else
-  #if JUCE_MODULE_AVAILABLE_juce_opengl && defined (MAC_OS_X_VERSION_10_14) && MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_14
+  #if JUCE_MODULE_AVAILABLE_juce_opengl
    #define GL_SILENCE_DEPRECATION 1
   #endif
 

modules/juce_graphics/native/juce_mac_CoreGraphicsContext.mm

@@ -41,12 +41,10 @@ public:
 
         auto numComponents = (size_t) lineStride * (size_t) jmax (1, height);
 
-       # if JUCE_MAC && defined (MAC_OS_X_VERSION_10_14) && MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_14
-        // This version of the SDK intermittently requires a bit of extra space
+        // SDK version 10.14+ intermittently requires a bit of extra space
         // at the end of the image data. This feels like something has gone
         // wrong in Apple's code.
         numComponents += (size_t) lineStride;
-       #endif
 
         imageData->data.allocate (numComponents, clearImage);
 

modules/juce_gui_basics/native/juce_mac_MainMenu.mm

@@ -455,10 +455,7 @@ private:
             {
                 addMethod (menuItemInvokedSelector,       menuItemInvoked);
                 addMethod (@selector (validateMenuItem:), validateMenuItem);
-
-               #if defined (MAC_OS_X_VERSION_10_14)
                 addProtocol (@protocol (NSMenuItemValidation));
-               #endif
 
                 registerClass();
             }
@@ -552,10 +549,7 @@ private:
             addMethod (@selector (validateMenuItem:), validateMenuItem);
 
             addProtocol (@protocol (NSMenuDelegate));
-
-           #if defined (MAC_OS_X_VERSION_10_14)
             addProtocol (@protocol (NSMenuItemValidation));
-           #endif
 
             registerClass();
         }

modules/juce_gui_extra/native/juce_mac_WebBrowserComponent.mm

@@ -375,7 +375,7 @@ private:
         auto flags = FileBrowserComponent::openMode | FileBrowserComponent::canSelectFiles
                     | ([parameters allowsMultipleSelection] ? FileBrowserComponent::canSelectMultipleItems : 0);
 
-       #if (defined (MAC_OS_X_VERSION_10_14) && MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_14)
+       #if JUCE_MAC
         if (@available (macOS 10.14, *))
         {
             if ([parameters allowsDirectories])