remove unnecessary casting between XGL_CHAR/char

Many of the changed lines are generated.  That should be fixed at some point.
diff --git a/tests/image_tests.cpp b/tests/image_tests.cpp
index 931af3d..e0bc62f 100644
--- a/tests/image_tests.cpp
+++ b/tests/image_tests.cpp
@@ -86,9 +86,9 @@
 
         this->app_info.sType = XGL_STRUCTURE_TYPE_APPLICATION_INFO;
         this->app_info.pNext = NULL;
-        this->app_info.pAppName = (const XGL_CHAR *) "base";
+        this->app_info.pAppName = "base";
         this->app_info.appVersion = 1;
-        this->app_info.pEngineName = (const XGL_CHAR *) "unittest";
+        this->app_info.pEngineName = "unittest";
         this->app_info.engineVersion = 1;
         this->app_info.apiVersion = XGL_MAKE_VERSION(0, 22, 0);