Rename Vulkan-source .h to .hpp

Also:
* Replace angle-brackets around including VulkanPlatform.hpp with
double-quotes.
* Remove unused Reactor/SubmoduleCheck/gtest/gtest.h

Bug: b/144825072
Change-Id: I2b68e7861355b30f93f23983e2cb97743a1bdf25
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/44389
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Tested-by: Antonio Maiorano <amaiorano@google.com>
diff --git a/src/WSI/VkSurfaceKHR.hpp b/src/WSI/VkSurfaceKHR.hpp
index 8636e2a..7e34712 100644
--- a/src/WSI/VkSurfaceKHR.hpp
+++ b/src/WSI/VkSurfaceKHR.hpp
@@ -17,7 +17,7 @@
 
 #include "Vulkan/VkImage.hpp"
 #include "Vulkan/VkObject.hpp"
-#include <Vulkan/VulkanPlatform.h>
+#include "Vulkan/VulkanPlatform.hpp"
 
 #include <vector>