Removed SDL_bool in favor of plain bool

We require stdbool.h in the build environment, so we might as well use the plain bool type.

If your environment doesn't have stdbool.h, this simple replacement will suffice:
typedef signed char bool;

test/testffmpeg_vulkan.c

@@ -321,7 +321,7 @@ static int findPhysicalDevice(VulkanVideoContext *context)
         uint32_t queueFamiliesCount = 0;
         uint32_t queueFamilyIndex;
         uint32_t deviceExtensionCount = 0;
-        SDL_bool hasSwapchainExtension = SDL_FALSE;
+        bool hasSwapchainExtension = false;
         uint32_t i;
 
         VkPhysicalDevice physicalDevice = physicalDevices[physicalDeviceIndex];
@@ -424,7 +424,7 @@ static int findPhysicalDevice(VulkanVideoContext *context)
         }
         for (i = 0; i < deviceExtensionCount; i++) {
             if (SDL_strcmp(deviceExtensions[i].extensionName, VK_KHR_SWAPCHAIN_EXTENSION_NAME) == 0) {
-                hasSwapchainExtension = SDL_TRUE;
+                hasSwapchainExtension = true;
                 break;
             }
         }